One small difference: protection warriors target enemies with their shield slam, while discipline priests target tanks (possibly DPS, but DPS is really only there to shorten the fight so you can go watch TV).
It's really not a new technique (in fact, it might be a stretch to call it a technique) but I'm likely the first person to give it a name. And I'm without doubt the first person to apply for copyright on that name...the law offices I contacted about it confirmed that (or so I interpreted their "You want to do what? Who would be silly enough to do something like that?").
Priests have a somewhat obscure ability known as Power Word: Shield. Discipline priests tend to use it quite a bit, though. In the latter stages of the previous expansion, they often tried to put it on as many targets as possible. It was the measure of first resort. Escalating mana costs (relative to mana pool) and a lowering of its duration effectively killed that strategy, but it's still something most discipline priests endeavor to cast on their target of main focus (like a tank) as often as they can (while, talented, it doesn't have a cooldown, it has an effective cooldown on a particular target due to Weakened Soul).
However, there are times when it's a better idea not to use it whenever you can on your main target. This has costs:
- Power Word: Shield is a pretty strong throughput spell (30-40k effective HPS on a target taking continuous damage with an instant cast, and up to 60k with the glyph)
- The Weakened Soul debuff it applies boosts healing from the priest due to talent
- A further talent, Rapture, provides major mana returns when the shield is broken (subject to an internal cooldown on the talent)
So when and why should you bypass these benefits? When you can expect a moment in time when any other spells (even Flash Heal) might be too slow or even impossible to cast and you can't count on other healers, you need to have Power Word: Shield in your back pocket, to slam the door on damage for a short time until you can restore stability.
Before I provide some examples, let me point out what I am definitely not saying: You should not normally treat Power Word: Shield as an emergency cooldown. Most of the time, you want to be using it as much as you can if you're tank healing. The improved throughput and mana efficiency (due to Rapture) usually make it an important ability to use as much as possible on your primary focus. Usually.
But This Is Not "Usually"
The first example I'll offer is being one of the two healers in the Alysrazor fight. I won't go through the entire encounter, as many, many...many guides exist for that. I'll briefly explain, though, the task of tank healing in phase one such that the reason to "shield slam" becomes evident.
In phase one, each of the two tanks is holding a Voracious Hatchling. Healing through the hatchling's normal melee is largely uneventful. However, they have two mechanics that can quickly make matters tricky. The first mechanic is Tantrum. The second mechanic is Gushing Wound. These two mechanics occur independently, which means they can (and often do) overlap. Or they can follow one another with no gap between them.
So you often have a case where you're letting your tank's health drop under 50% and then dealing with an enrage, essentially. The hatchlings hit rather hard and rather fast at that point, so if the tank's health is under 50%, there is the risk of losing the tank.
This is a good time to shield slam. Let the tank's health drop below 50%, causing the debuff to drop off, and then instantly drop a shield on the tank, shutting off the Tantrum damage for a precious few seconds. Your tank's buffer is not really his/her health. It's the time left before the tank dies. The sub-50% health is part of it and time provided by stopping the damage is the other part, which is why mitigation and absorption are so valuable. You're essentially increasing his/her effective health, which is crucial in a dicey situation like that.
Shutting off the damage gives you time to catch up, after artificially being forced to fall behind. There are other ways you could handle this (for example, not letting the tank drop below 50% and healing through both Gushing Wound and Tantrum until Tantrum ends) but that's less mana efficient and waiting for Gushing Wound to drop allows you to quickly throw a heal on someone else if necessary. And if the Tantrum follows directly after a Gushing Wound, even that is not an option.
Moving on to another example, let's examine how my guild does Baleroc. What I've heard is that the Shards of Torment are supposed to spawn in melee, but that's not what we were seeing. They appeared to spawn on random players, whether they were in melee or at range. Ultimately, we dealt with that by having two stack-up spots...we all--tanks excepted--started on one on those spots, when a new shard of torment had been announced and was soon to spawn, we all moved en masse to the other stack-up spot except the next DPS in rotation to soak the shard. Each subsequent shard, we repeated the maneuver, moving back and forth between stack-up spots.
We may have missed something crucial, but this is the behavior we were seeing for shard spawns, so we adapted that strategy to deal with it and it's worked for us. It did, however, have one important consequence: healer movement.
On every shard spawn, every healer was in motion. This was a problem when the tank taking the Decimation Blade strikes had just been...struck. Suddenly the tank is around 10% health and has to be pushed back up to about 100% health before the next strike arrives, and all the healers are moving.
This is an ideal time to use what I've dubbed "shield slam." You may have noticed that the tooltip for Decimation Blade said that it ignores mitigation effects. Mitigation refers to effects like "take 10% less damage." It doesn't apply to good old absorption, and Power Word: Shields will absorb Decimation Blade damage. With a large Vital Flame buff, those shields can absorb a great deal of the Decimation Blade. Therefore, dropping it on the tank just before you move, ahead of the strike, means that you (and your fellow healers) arrive at the destination with significantly less damage to heal up (which is good, since the movement also means you have less time).
Slamming The Door (On This Article)
I've gone through a couple of examples of when you want to limit using Power Word: Shield so that you can use it at crucial moments. The specific examples may not apply to you, depending on how you do those fights or whether you're doing those fights at all, but the concept is still worthwhile.
Often times, maximizing the uptime of powerful abilities is most valuable. They have cooldowns (of one type or another) for a reason: the more often you can use them, the more powerful you are and therefore Blizzard doesn't want you using them too often. However, maximizing uptime is not always ideal. Sometimes, you want to maximize the leverage of something...that is, maximize the value by using them at the specific times when they'll count the most.
To use a baseball analogy (skip down to the next paragraph if baseball, analogies or baseball analogies bore you), it's the difference between maximizing a pitcher by getting the greatest number of innings out of him or by maximizing the leverage of the innings he does pitch. Starting pitchers are an example of the first...they throw as many quality innings as they're capable of and maximize their value that way. Relief aces are an example of the second; they throw many fewer innings but they come into the situations that you know have a major bearing on who will win the game (close game, near the end) which reduces the frequency of "wasted good innings" like a shutout third inning of a 13-2 game.
Most of the time, you want to maximize uptime of Power Word: Shield. But be alert for those times when you'd rather maximize the leverage of it. Shield slam to victory, the priest way.