What are your sources on the 30% coefficient? I tried to look it up on EJ but could not find anything.

I mentioned that shielding is hindering rage/mana generation for thanks. It’s somewhat hidden under “Weakness”.

First thing? If you consider damage prevented to be similar enough to health gained, you can argue that Power Word: Shield has one of the lowest HPM (Health Per Mana) of almost every healing spell (other than Flash Heal, I believe). As a result, you are more mana efficient actually casting a healing spell than this. Furthermore, it only benefits from 30% of your Bonus Healing (as of patch 2.3), which means that it scales worse than staple healing spells like Greater Heal (87%) and even Flash Heal (42%) as you get more Bonus Healing.

Secondly, Power Word: Shield is only beneficial if it absorbs damage. If it doesn’t, you’ve managed to waste up to 600 mana. Since its use is only limited by the Global Cooldown and your target’s Weakened Soul debuff. In other words, you could easily go through an entire raid and spam it on every person — but it’s only effective if it prevents those people from taking damage.

Far too often I’ve seen my fellow priests bubble player after taking minimal spell damage and then have the shields wear off without any benefit. A lot of this is reliant on experience, since understanding and being familiar with a boss encounter can let you know when the optimal time to use the spell is and who it would be best cast on.

Wonderful points on the talent! A little wrong on the exact amount of benefit it gains from Bonus Healing, but you’re only behind a couple of patches (it used to be 20% and 10% even before then!). One other thing I’d note in any description of Power Word: Shield is how this can adversely affect rage generation; since the bubble prevents damage, rage cannot be generated. It’s not as much of an issue once you progress further in raiding, but for those who rely on rage (whether red or blue!) a bubble at the wrong moment can have adverse results!