LOL, I only shield pally tanks - and only when we are standing before a mob or group of mobs I know can pop it within a few seconds. (The exception to this is during boss special moves - like Kael's fireball. It just makes good sense to give anyone who might eat that kind of damage an extra 3kish EH.)
PW:S + PoM + Renew all cast before his AS leaves his hands means I'm not in combat for those few crucial seconds while that room of mobs runs around the corner after him and into his consecration ticks. If we are just pulling a normal heroic boss then PoM+Renew seems better, since as was mentioned, PW:S returns no mana and most heroic bosses really don't hit that hard on plate. Trash is generally more dangerous. (Especially when you pull several groups at a time!)
And yes, PoM returns mana when it bounces. The threat applies to the target but the heal is recorded as belonging to the caster in the combat log. Unless the tank is taking such outrageous damage that the GCD can't be spared I use it everytime the CD is up, as it means more threat for him and less for me
Not that threat is much of a problem. Unless it a mob has broken CC or no one has actually hit it yet, I'm not going to pull aggro.... and if I do fading while running into consecrate (and PW:S myself) usually fixes it - and no doubt a taunt on behalf of my well-armored buddy.
I can't think of any reason (other than as was mentioned for boss special abilities that could instagib) to cast an in-combat PW:S on a tank. It doesn't mitigate much more damage than a PoM, and takes the same amount of time to cast as a flash heal... I'd rather use that GCD to try and get a big heal off.
Though PW:S are great for overenthusiastic mages
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That's just my opinion though. If a tankadin asked me not to shield him I wouldn't - and if he right clicked it off I wouldn't shield him again. Otherwise I do so on my own discretion.
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