Quote Originally Posted by KarstenS View Post
One word: Mana efficiency.

Healing through damage is in nearly every situation more mana efficent than pre shielding, as long the incoming damage < full life.

Point 1 is: Small heals and HoTs cost always less MP per HP than bigger heals/heals with shield

Point 2 is: Pre shielding is usually done by heals with shield effect (exception: Stoneskin). In the most cases this heal is going to be 100% or close to 100% overheal. -> Wasted mana.
Note that the context for mitigation that I made was with diurnal AST being able to collective and disable to mitigate damage whereas a WHM cannot. In that case, while a WHM can get through heal checks through raw healing, an AST can do that with a combination of raw healing and mitigation. The following posts with math by mp-please shows that. Which is why mitigation and raw healing go hand in hand.