Well, except for that spirit wand, right? Surely that...no self-respecting mage or warlock would want it, with 60%* of a secondary stat completely useless. Only a priest would want it...only a heali...
*Reforged
Well, there's the rub. A shadow priest would like it just fine, since spirit can be converted to hit for any ranged DPS spec that's part of a hybrid class.
So why does that matter? Isn't the spirit wand still healing priest loot, even if a shadow priest can use it, just as any spirit gear is healer loot even if other DPS specs can use it? And, for that matter, as healers become less beholden to their blue bars, isn't any intellect gear they can wear that contains no hit rating also perfectly viable healer loot?
Hello. I'm a healer. And in all of those cases, my answer is a categorical no. That's why I took a bold step.
In our raid group, we have a very, very simple loot system. It's round-robin. We maintain a loot list and when you get a piece for your main spec, you drop to the bottom of the list. The list adjudicates who gets a piece when multiple people want it. Highest person on the list receives the loot. It's meant to be fair, impartial and distribute loot relatively evenly across everyone.
And I want no part of it.
Thus we come to my bold step: I asked to be removed from the hallowed loot list.
The consequence of this is that it's never "my turn" for loot. Anyone else in the raid has a higher claim than me, by this decision of mine. I'll still receive upgrades, but only when no one else needs the piece.
Am I just that noble? Well, yes, I am. However, it's for a reason that I feel is perfectly rational. The subject of which shall be meat of this post.
Defense Sells The Tickets, But Offense Wins The Game
For those of you not steeped in the ceaseless avalanche of cliches that is sports commentary, there's a popular saying that "offense sells the tickets, but defense wins the game," suggesting that people enjoy watching scoring but ultimately preventing scoring by the other team (the "less glamorous" role) is what matters most.
I'm here to tell you, that it's reversed in World of Warcraft. If I were to craft a pithy maxim that makes sense within the context of the game, it would be "Healers* win normal modes, but DPS wins heroics."
*When I say "healers" here, I actually mean "tanks and healers." It's just not as pithy and catchy when you throw in "and tanks."
The reason for this can be summed up in two words: enrage timers. Heroics, pre-nerf at least, tend to have hellaciously tight enrage timers. This is why many raid strategies for heroic modes advise raids to cut healers and tanks wherever possible, to pack in more DPS.
When doing normal modes, you're learning the basics of the fight for the first time. Tanks and healers are the most important for this step, because they extend the raid's lifespan. The longer you live, the more of the fight you see and the more practice you get. Go healers!*
*And tanks
Once you mosey on into the heroic modes, though, the focus changes. You mostly know the fights. The heroic modes have somewhat different mechanics, but most of the original mechanics are still there and the concept of the fight is usually very similar. You might want a few "Just survive as long as possible so we see the new mechanics" wipes, but you don't gear around the first few looks at the fight. The main thing is the DPS. It must be high...very high. Obviously, everyone is going to have to play well, but the fights really shift away from healers as a main focus. DPS must beat the enrage timer and everyone must avoid as much avoidable damage as possible. That's the design of heroic modes, it's how they're balanced.
Therefore, "getting over the hump" means getting DPS geared enough to beat the enrage timer. After that, gearing up healers certainly helps...the stronger the healers are, the more margin for error the raid team has. But no healing team is going to make up for the "didn't beat the enrage timer" error.
Healers Cannot Reach For The Stars
Remember when our mothers and fathers told us that we could rise as high as we wanted if we worked hard, that there was no limit? They didn't mean healers, they only meant DPS.
DPS has an infinite horizon. You can always do more DPS. More gear, more skill, more buffs will all equal more DPS. Further, you can do more DPS and that unholy death knight you hate can also do more DPS...at the same time! It's not zero sum...one person doing more DPS doesn't lower the ability for someone else to do DPS.
The healing game is very different, for three key reasons.
One is that there isn't infinite capacity to heal. A healing team's healing output is strictly capped to the amount of damage done to the raid team by the boss (and his or her minions). You cannot heal damage that doesn't exist. If a raid boss does 21 million damage over the course of an encounter, the maximum healing the team can do is 21 million.
Number two is that as your raid team gets better at the fight, the damage taken is going to go down. Some damage is unavoidable but lots of it is not, a design choice aimed at making dance skill matter. The better you do the dance, the less damage you take. So as time goes by, that maximum amount of healing available to be done shrinks, leading to lower output from healers.
Finally, healing is a zero sum game. Since healing to be done is, as established, a capped resource, every healer in the raid is competing for a piece of it ("competing" in a literal sense, not necessarily from an attitude point of view). One healer pushing their healing up massively simply diminishes the possible output of any other healers in the raid. All the healers cannot simultaneously heal significantly more unless they were woefully over-matched from the start.
So when you have one group of players (DPS) who can turn gear into bigger and bigger output and another group (healers) who cannot, it makes a lot of sense to bias the gear distribution in favor of the group who can convert it into no-questions-asked larger output.
Personal Reasons Are Personal
While the idea that DPS can use gear upgrades more powerfully than healers is the large majority of why I made the decision to remove myself from the loot list, there was another reason that was simply a personal choice (which is why I'd never even suggest to my fellow healers that they do the same as me).
I want to de-emphasize loot for myself. There have been times when I've been frustrated over not getting the piece I need to drop, or losing it to someone else. I know, though, that loot is not why I play. At least, that's what I believe. WoW Insider had an article a month or two ago (I'm too lazy to find it and link it) about how everyone, at base, is motivated to raid by loot. The writer said (paraphrased), "If you don't believe that you are [motivated by loot], ask yourself how long you would raid if you never got a single piece of loot."
Not long, but I think that's a meaningless question. Never getting loot is the same as never raiding, because you'd soon no longer be geared enough to raid. Loot is necessary simply to be able to raid. The question is how much you're motivated by the Gollum-like desire for shinies.
But we wants it! We'll reforge the expertise to spirit!
So a better question is, "How long would you raid if you were always the lowest priority for loot?" That's what removing myself from the loot list accomplishes: placing me at the lowest priority.
I'm just kidding. I don't really tend to do "how to" guides (because so many are available online) and monks aren't completely fleshed out, to say the least.
That said, enough has been revealed about monk healers that it's time to look at the basics and speculate wildly about the rest. Commence speculation, gogogogo!
Melee Healers
It appears that there will be two aspects to being a melee healer. One is that you must be within melee range of your healing targets for direct healing (or at least, nearby). The other is that apparently you'll have access to indirect healing through melee attacks on enemies.
Being a "melee healer" (that is, a healer who works at melee distance rather than from range) was one of the few areas that existed for Blizzard to expand into to create a new style or niche of healing. There was some very rudimentary (and ultimately non-existent) form of being a melee healer in the holy paladin role, as Seal of Insight refunded health and mana to the paladin if he or she stood in melee range of a mob and hacked away. It didn't prove to be worth it enough for paladin healers to actually melee mobs and bosses in instances, though, as paladin healers pretty universally stood at range like all other healers.
It wasn't clear, then, what mechanics would enable a healer to stand in melee. The mechanics would have to make standing in melee essential to being successful as a healer and, further, feel rewarding as a play style. Rogues stay in melee range because their DPS depends on it and because it feels fun to position themselves for blade attacks. It has to be both necessary and fun.
What little we've heard from Blizzard about monk healers (Mistweavers) starts to fill in the road map for how Blizzard believes these two goals can be accomplished for a healer. It seems to hinge on two key concepts, so let's look on them. (Don't worry, wild and baseless speculation is still ahead!)
Mobility
Since Mistweavers will apparently need to be nearby allies that they are directly healing, mobility is a must. Melee classes like warriors and rogues have crucial mobility abilities, like Heroic Leap, Sprint, Intervene, etc. This makes sense since melee classes have much stricter positioning and range issues than casters and hunters.
Mistweavers will have much stricter positioning and range issues than other healers, so they're going to need the mobility help as well.
Meet Roll (for any linked monk abilities, I'm linking the battle.net page on monks, which has three sample abilities). The description is pretty bare bones, reading only "Roll a short distance." We can envision this, however, being a fundamental way to quickly get from one place to another, perhaps equivalent to a mage's Blink (minus the "poof" graphics). It has no stated cooldown, though it has a cost in chi. Blizzard has already stated, during Blizzcon, that Mistweavers will use mana instead of chi, so it remains to be seen what the cost is in mana.
Of course, the possibility also exists that Roll won't be available to Mistweavers, but that strikes me as implausible and silly, for the reasoning stated above that melee-based healers will need mobility. More likely, all abilities will cost chi as baseline, but will all have their costs transformed to mana when you spec Mistweaver.
I'd expect more movement-enhancing abilities, because you can't ask a healer to have extremely tiny ranges to their direct healing spells and then expect them to walk around, using their own legs like suckers. Without things like Roll, the message is "Roll a healing class that has sensible cast ranges."
That said, if there are a number of movement-enhancing abilities, we start to see an interesting play style emerge. A cross between a protection warrior (for whom getting around the battlefield quickly is a forté) and perhaps a restoration shaman (the healing spec that has the most demanding positioning requirements). Zip around the battlefield healing small knots of allies. The melee clump here, a ranged clump there, the dying-in-fire clump...no wait, never mind.
Statues
Healing props are nothing new. Restoration shamans have had a multitude of totems forever. They lose totems in the couch cushions and groan when totems muck up the washing machine because they left them the pockets of their jeans by accident.
Totems have generally provided either a passive buff (long-lasting totems that just buff everyone in range) or active effects (short-lived totems that do something like damage, mana restoration, taunting, etc).
Statues are something in between. They don't, in and of themselves, provide a buff or an active effect. What they (and by "they," I mean the one statue that has been revealed so far) appear to do is act as a proxy, allowing the monk to act through them from a distance.
Summon a statue at the target location. Anytime you deal damage, a nearby friendly target within 20 yards of the statue will be healed. You can have up to 3 Jade Dragon Statues active at a time.
A quick note before we go into consequences of this specific statue. Do we have a misprint or a hint of things to come in the "You can have up to 3 Jade Dragon Statues active at a time?" The name of the spell contains "Jade Serpent" not "Jade Dragon." That suggests that either they typed the wrong thing for that sample tooltip or else "Jade Dragon" is a class of statues, of which the Jade Serpent statue is just one. Interesting, though it doesn't tell us much except there may be a whole statue system rather than just one or two statue spells.
Looking at this specific spell, though, we see perhaps the other foundation for a melee healer...agents that can allow you to act "in melee range" in different locations. You're standing next to the boss, spin-kicking it happily. Your glass cannon mage is about to shatter from the stress of all the DPS he or she is putting out, at a far-away location. You either have a statue there or you quickly put one there*. Your next spin-kick gets turned into healing energy and flows to the statue at which point it's redirected into the mage, filling his or her health bar and the DPS continues uninterrupted.
*Note that the statue is summoned at a target location, suggesting that there is a range for dropping the statue rather than the statue dropping where you're standing like shaman totems
You didn't have to move away from the tank and melee clump you were healing with your direct healing spells. You just had to shift from acupuncturing your melee mates to delivering crane kicks to the boss' jaw in order to deliver heals to someone nowhere near you.
Crazy Speculation
If the "Jade Dragon" language really does imply classes of statues and therefore an entire statue system, what else might statues do for us? We want to avoid statues being totems by another name, so we want to keep our thoughts away from passive buffs (like added armor) or active effects (like summoning a temporary pet or shooting fireballs) and think more in terms of them being agents or instruments of the monk's will.
Here's an example: Statue of the Cloud Serpent
Summon a statue at the target location. Anytime you deal damage with a Death Monkey Super Kick, you will be teleported to the statue. You can only have 1 Statue of the Cloud Serpent active at a time.
(Death Monkey Super Kick is just a place-holder for a baseline monk attack. It may not be called that.)
This allows you to use one of your fancy monk attacks to instantly jump to another place (like a stack-up spot or a place across the raid encounter room where a second group is fighting another member of a "council" type of raid boss, etc), the better to get around the battlefield.
It's just an idea, the type of thing that I feel makes sense for a statue system that would differentiate it from the totem system. Agents in the field..."my statues r in ur raid, spying on u."
Also, monks can use fist weapons in addition to one-handed swords, maces and axes. Might we finally see the first sanctioned dual-wielding healing spec? Almost certainly not; Blizzard is very conservative in some ways and clearly has their own conceptions of what each role "looks like," and I don't think dual-wielding healers fit their mental models. For a short time, restoration shamans were going deeply enough into the enhancement tree to pick up dual wielding in order to dual wield spellpower weapons (back when dual wielding was a talent and you didn't have to invest 31 points into a specific tree). Blizzard shortly thereafter made all one-handed spellpower weapons "main hand," rendering it impossible to hold one in the off hand. They also made talent tree changes to crack down on inventive "hybrid specs" that produced results that Blizzard hadn't planned on.
So, my guess is that they don't like the idea of healers dual wielding and will not be producing any spellpower weapons that can be equipped in the off hand. They will probably also lock dual wielding to the DPS and/or tanking specializations, to avoid any experimentation with an agility off-hand to increase damage done (and, therefore, Jade Serpent healing done).
Even still, one can hope. Hope brought us Azerothian Pokémon transmogrification.
Melee Healing--Just Right Crazy Or Not Crazy Enough?
There's a strong chance this won't work. Remember, they had a "new concept" in mind with their last new class, death knights. That new concept was that you could tank or DPS in any spec, with the presence you used being the most important signifier to your role. That proved to be a bear to balance properly and they ultimately decided it was a failure and reconfigured death knight specializations more traditionally, with a dedicated tanking tree and two DPS trees with a different playstyle each.
So they may decide over the course of 5.0 that melee healing is a failed concept as well and eventually Mistweavers will join their other healing brethren at the perimeters of the fight, shying away from contact. They may even decide that if melee healing isn't on, then there's no point even having a monk healing class (because what would it bring that all the existing healing specs do not?).
So if you enjoy healing, spend some time playing a monk this next expansion. You'll get to see at least one vision of what melee healing might look like and the chance to play a monk healer may not last forever. There are some interesting concepts shaping up for Mistweavers, based around unique mobility, damage dealing and proxy healing. It may work, it may not, but you may want to have seen it for yourself before Blizzard makes their ultimate determination and either changes the spec or eliminates it for another DPS spec.
Just don't get too attached to the spec, as our rather Buddhist Pandaran friends would advise.
In case you don't get the (old) meme reference of my post title:
Okay, now that that's out of the way, let's talk about "healing space." This is not an alternate zone that healers live in, perhaps like the Emerald Dream area in the Valthiria Dreamwalker encounter. This maps out where each healer excels, when able to do what their class abilities optimally allow for, to create maximum synergy between the healers in your team.
This is much more crucial in twenty five man encounters, when you have more healers and significantly more overlap. It does happen more often in ten man encounters that healers get isolated more on their own healing islands, in which case you cannot "specialize" as much. However, as you push into heroic modes, even ten man raids are well-advised to try to organize the encounters such that all the healers you're using can cover all the same targets (everyone). This is not always possible but, when it is, that's where heal space analysis is valuable.
The long and the short of it is that if two or three healers can cover the same targets, you maximize their effectiveness by A. making sure the two or more healers have complimentary powers and B. having each healer bias their spell usage toward specialization.
So what heal space does each class inhabit? Let's take a look.
Note: The next four sections are a quick look at what constitutes the core of each healing class (and spec, in the case of priests). If you would find a run-down of these class-specs dull, skip past the sections with class headings. None of those sections contain theory, just my views on what (essentially) makes each class-spec unique. That "healing world view" is important to the theory that comes later, of course, but I don't believe my healing world view is controversial.
Druid
For the last (large number here) tiers, druids have been the reigning overall healing throughput champions. With their "creeping heals" (my term for healing that's always creeping upwards, everywhere, all the time), they're almost like the inverse of a damage aura...they provide a healing aura (as it feels from the outside, this is in no way to suggest that it's passive on their end) as everyone's life bars are always moving upwards thanks to them. They can Rejuvenation blanket when everyone's taking AoE damage, Wild Growth on cooldown, Swiftmend to create a healing circle under a group of people and keep potent HoTs (the aforemention Rejuvenation and Lifebloom) rolling on the tank(s).
And then, of course, there's always the raid healing bomb of Tranquility lurking.
The reason druids have been such potent raid healers is because they're not provided any absorption or mitigation abilities (leaving aside the personal cooldown, Barkskin, which is of only niche value to a restoration druid). Their contribution is entirely wrapped up in moving life bars, so they move them a lot.
While they can use direct heals to keep someone, like a tank, alive through continuous damage, it's not where they excel and it's not the optimal use of their mana. "Optimal" is the crucial word for this analysis, since we're trying to maximize a healing team.
Paladin
For the last four or so tiers, at least, paladins have been somewhere between very strong and broken-strong (ICC days) as tank healers. They've been given some new tools in Cataclysm (notably, Holy Radiance and Light of Dawn), but neither has changed the fact that the bulk of their work is done with strong single-target throughput. Their healing space will probably have to be re-evaluated once patch 4.3 arrives, due to the major changes to how Holy Radiance will work.
Holy Radiance (thus far) has been constrained by a cooldown, making it unspammable, and Light of Dawn is a holy power release, so it's also unspammable, since they need to build up holy power in between usages.
That leaves paladins the most beholden to the "Three True Heals" model that Blizzard has tried to build into every healing class (with varying levels of reliance across classes). Since their "quick, mid-level heal" Flash of Light is not generally considered a good use of mana, they end up heavily reliant on four spells with a heavy emphasis on the first two (being the ones without a cooldown or holy power requirement): Holy Light, Divine Light, Holy Shock and Word of Glory.
So direct heals are what paladins will be dealing in, largely.
Shaman
Shamans have an interesting concept. The majority of their healing is direct, though they also use an area HoT (Healing Rain) and a more traditional HoT that procs from one of their main direct heals (Riptide).
What makes shamans interesting is their mastery, Deep Healing. The upshot of their mastery is that the lower health their healing targets, the more powerful their healing spells are.
So shamans are a mixture between direct healing and healing over time, with potency inversely related to the health of their target.
Priest
Priests come in two flavors, of course. There is the Discipline flavor and the non-Discipline flavor (I kid, I know that one of the healing trees is named Holy, even if Blizzard doesn't).
Discipline priests have always had a unique mechanic (which holy paladins have recently infringed upon with their mastery, but not very successfully except in niche cases) known as absorption. These are shields that absorb some of the incoming damage before it can affect the player. Shields are the centerpiece of the discipline spec. And while discipline priests (like all healers) have an assortment of direct heals, the other thing they have which is more or less unique to them is mitigation. This is similar to absorption, in that it prevents damage rather than healing it, but rather than absorbing it, it reduces the degree of the damage by a percentage basis. So instead of absorbing 45,000 damage, it will reduce the incoming damage by 10%. One of their signature mitigation spells is a tank cooldown, Pain Suppression.
Holy priests on the other hand do very little absorbing and mitigation. They are more similar to druids in that they use healing over time and direct heals to do lots of healing over the encounter time. While druids bias more toward HoTs, holy priests bias more toward direct heals. Unlike druids, holy priests do have a potent tank cooldown, Guardian Spirit. As you might notice, Guardian Spirit is kind of the reverse doppelgänger of Pain Suppression. While Pain Suppression mitigates damage by 40% on a target, Guardian Spirit allows for 40% more healing on the target. Guardian Spirit has the added benefit of preventing a death, which does make it a bit more powerful but also compensates for prevented damage being less risky than healing damage after the fact, a factor that makes damage mitigation more powerful than a healing boost.
Healing, Economics...Same Thing
If all of that was a fairly old hat recap of the healing class-specs, I apologize. In terms of structure, I felt it was important that we establish what each healer is doing at his/her core before we start parceling out territory in the healing universe.
The central concept of healing space is this: While every healer can do a variety of things and fill any role, especially direct healing of all the things, the highest efficiency is achieved by each healer focusing on the things they do best and avoiding the things they don't do as well as another, even if they can do it well. If you've studied economics, this should be a pretty familiar idea, because it's mirrored perfectly by the idea of Comparative Advantage. By specializing in what you do best (rather than doing everything you do decently), you increase the efficiency of your team. To make the parallel to the economic theory, if you analogize your healing team to a world economy, your healers are trading products (throughput) for currency (mana efficiency) with each other.
The economic theory of comparative advantage is wonderfully counter-intuitive to most people when they first encounter it. It generally isn't an immediately obvious idea that, even if you're good at a number of things, if you exist in a world with potential partners who do anything better or worse than you you're better off specializing rather than doing everything you're good at.
Blizzard made sure every healing class can fulfill any role competently with the advent of Cataclysm, because they didn't want raids to feel locked into specific class make-ups rather than just bringing the people who were either best or else they most enjoyed playing with. So the changes they made to achieve this made every class a jack-of-all-trades to a certain extent. However, they didn't give every class and spec every ability or equalize their power in every role. They just ensured that every class and spec reached at least a minimum baseline in every healing role. This leaves enough difference between the class-specs to leverage for the sake of efficiency (and when I say "efficiency," I mean optimizing throughput for a healing team).
So how do we leverage this? To put it very simply, we identify where each class-spec's best use of mana lies and create a healing scheme whereby each healer is biasing their spell choice heavily in favor of that best use of mana. That is optimizing healing space.
This may sound like what healers should always be doing, but it's only possible in group play in which there is more than one healer. In a five-man environment, for example, where there is only one healer, you cannot specialize. You must cast all the spells necessary to keep everyone alive. This means some amount of direct healing as a druid, for example, even if direct healing is not your forté, because HoTs alone aren't going to keep a tank up through heavy damage. The economic theory of comparative advantage is useless if you are alone on a desert island, and optimizing healing space is worthless when you are a healing island in a five-man group.
No, it gets interesting when you are in a ten man or, especially, a twenty five man raid. The larger the group, the more healers. The more healers, the more specialization each healer can engage in, because a lot of niches can add up to a coherent whole. A single niche is just a niche.
Establishing The Foundation Of Healing Space
I primarily raid in ten man groups, so I'll primarily use that as the example. However, I'll note how this really flourishes in twenty five man groups at the end.
My raid group generally employs a healing team of a restoration druid, a holy paladin and a discipline priest (hey, that's me!). This has actually often been called the "holy trinity" of ten man raid healing teams and for good reason as we'll see from a healing space analysis. How do we leverage these three classes optimally?
The simplest approach for a healing team is what I like to call "see damage, heal damage." If someone is below full health, cast the appropriate spell (factoring in time urgency, amount of healing needed and mana efficiency required). This isn't particularly organized but it can actually work, especially if the healing team is extremely familiar with one another. The primary drawback here is that the disorganization can lead to sub-optimal healing: multiple healers addressing the same damage (leading either to overhealing or else a healer canceling their spell mid-cast, wasting some amount of time) and certain targets not receiving heals quickly enough.
One step up is straight healing assignments. Healer A will heal the main tank. Healer B will heal the off-tank. Healer C will heal all the non-tanks. This is much more structured. Overhealing will be reduced because, at least notionally, healers are not cross-healing the same targets. Every target has their dedicated healer and thus knows exactly what healing that target is receiving because it all comes from himself/herself. The primary drawback here is that overly strict adherence to assignments can leave healing potential on the table (Healer A being idle when the main tank is at full health while Healer C struggles with a burst of raid damage) and deviance from assignments leads to a greater and greater descent into the previous "see damage, heal damage" paradigm, with its own attendant drawbacks.
While the second option (assignments) is generally better regarded, each paradigm actually has its strengths. "See damage, heal damage" ensures that all the healers are capable of remaining active at all times (at least, all times in which there is damage to heal) which prevents useable healer casting time and mana regeneration from being wasted (a healer sitting at full mana is wasting all their itemization and talents that provide mana regeneration), while assignments provide the structure to keep healing from being wasted.
The ideal situation would be to marry the strengths of each paradigm into one, without also importing the attendant weaknesses. A healing space paradigm does just that. Let's look at how this works.
Crafting Healing Space
A restoration druid, as we noted, is best at keeping continuous healing "growing" on lots of targets at once, whether that's through Rejuvenation on multiple targets, Wild Growth or Efflorescence parked below a stack of raiders.
A discipline priest excels at preventing incoming damage.
A holy paladin is most powerful at pumping out strong direct heals on single targets (the value of which is amplified by their "reflection" mechanics, Beacon of Light and Protector of the Innocent...much as a battery of mirrors serve to focus and intensify a laser beam).
So we craft a healing space in which:
The druid does keep her HoTs "growing" on as many targets as she can sustain and/or makes sense for the encounter but does not cast many single target heals.
The holy paladin does cast her powerful single target spells on targets who are either particularly under siege or else are particularly low but does not concern herself with damage prevention (gears away from mastery) or heals over time (Holy Radiance, which has a mana opportunity cost).
The discipline priest does cast her shields and mitigation spells often to slow the damage on targets likely to take damage in the near future, but does not spend much time or mana casting HoTs or direct healing spells.
A crucial point here is that there are no explicit target assignments. You are not assigning the holy paladin to one or both tanks and the discipline priest to one or both tanks. You are not assigning the restoration druid or the discipline priest to raid healing. Instead, if you'd like to think in terms of assignments, you are assigning each healer to a specialization.
A discipline priest is optimally using his mana when he casts a shield likely to be consumed by incoming damage. A restoration druid is optimally using his mana when he casts HoTs (whether single target or multi-target) that are likely not to go as overhealing. A holy paladin is optimally using his mana when he casts a powerful direct healing spell on a target at a low enough health that little of the direct heal goes as overhealing, and the target of the heal reflection also is low enough health that little of the reflected heal goes as overhealing.
The result is that, as long as there is damage to be healed, you have healers who can be active and engaged, yet there is implicit structure that minimizes the overhealing that chaos can cause. The druid is a champion of overall healing, but all that creeping healing is useless if targets die before they can tick back up to a safe level. That's where holy paladin direct heals come in, swiftly (relative to druid HoTs) pushing a dangerously low target back to a safer level where the slow healing over time can finish the job passively. But the paladin's big heal is useless if the target dies before the heal lands (or before the paladin can find time to cast on that particular target). That's where discipline shields come in, providing an instant buffer on targets in critical condition, keeping them afloat until the healing of the paladin and druid can save them.
At a more abstract level, the discipline priest provides a preventative umbrella over everyone, underneath which the druid's garden of HoTs provide a "healing aura" constantly moving everyone upward and the holy paladin combats spikes downward in health to anyone with spikes upward in health through spells.
In Conclusion, More Explanation
In this healing space, each healer has a clear-cut role, which allows them to fluidly move between the same targets, but in their own space. Think of it as a separate dimension...each healer is their own island, in their own dimension. You, as a healer, are responsible for everyone...but only within that dimension. As long as every healer optimizes the throughput of the spells that make up their dimension, the healing team is optimizing their overall throughput.
Except when necessary, you need to resist moving into a fellow healer's dimension. Each time you do so, you detract from the efficiency gains. Your healing team has only so many GCD's (global cooldowns) and mana to work with over a given encounter length. Using your GCD and mana to address a small bit of damage on a target, when a druid's HoTs can address it, may seem harmless enough, but it's a GCD and mana you could have used casting a Power Word: Shield. On a one-off basis, it doesn't matter much...but these little decisions add up over the course of the encounter and undermine the benefits of specializing within the crafted healing space.
For the sake of brevity (this post is barely more than a haiku in length and I like that succinctness), I won't go through a similar healing space crafting for every combination of healing classes. But you can see the format: identify what a healer does that is an optimal throughput use of their time and mana and give them that specialization across the entire raid and task them to use non-optimal spells as little as possible. A shaman, while not included in my example healing space, can easily be crafted a space based on their unique power on low health targets. All that's necessary to create these types of healing spaces is multiple healers. There can even be duplicate class-specs as long as each of the duplicates can, through talents, gearing or playstyle, provide a different specialization (two holy priests can each specialize differently based on different chakra states, two discipline priests can provide absorption and direct heals, etc).
The key is for each healer to decide, for an encounter, what they will be spending their mana on, working to make that efficient (through itemization and talents) and then sticking to it as much as possible. If you've geared and talented for making your direct heals as powerful as possible and then bias your spell choice heavily to direct heals, you can achieve a lot more than spreading your gearing and talents out and trying to do lots of different things...as long as other healers are picking up the other forms of healing.
As I mentioned previously, this can be taken to an even greater extent in twenty five man raids, where instead of two or three healers, you're working with five or six healers. Since every healer is still responsible for everyone, you handle more healers by breaking healing space into even more granular roles. How about a holy paladin who specializes in stacking mastery for absorption and focuses on overhealing targets to build up larger and larger bubbles on targets she expects to take big damage soon? That's happened in some world-ranked raid groups. How about a discipline priest who stacks crit and haste in order to pump out Prayers of Healing to coat the raid in Divine Aegis bubbles (since Power Word: Shields can't have constant uptime due to Weakened Soul)? These are the types of niche roles that ten man raid healers simply can't afford to try because it's too small a niche for the roughly 33-50% of the total healing you're responsible for. The more healers, the more specialized you can afford to be and the more specialized your healers must be to fully leverage each healer.
I'm Done, Thanks For Reading
We are here to protect you from the terrible secret of (healing) space.
