Originally Posted by
Bigslick
3% damage reduction can be provided by Blessing of Sanctuary, and 6% more healing on target (which only boosts YOUR healing to the target) is provided by Tree of Life form, and these effects do not stack.  Basically, if you have enough pallies to put up Santuary and you have a resto druid, these benefits are gone.  Same w/ the IDS spellpower buff being provided by shaman totems.
Disc priests do provide for higher average effective total health on their target by damage mitigation, though, and do provide the +80 spirit buff which translates into better regen and, for certain specs, increased spellpower through talents.  That plus the fact that it's not terribly difficult to build up enough int to where it's about impossible to run OOM in a raid (running at ~ 25k mana pool raid-buffed now, and have zero mana issues even when the holy priests are crying for innervates despite being in group w/ shaman providing mana totem (ok, to be fair holy is pretty efficient in its own right,  provided they have the opportunity to get outside the FSR - which does NOT happen on fights like Patchwerk).