Stoneskin should only be used in a handful of situations:
1) prepull on everyone
2) mitigating a large damage mechanic that is unavoidable
3) if you have nothing else to do and your MP is full
Stoneskin is not MP efficient. Nor is stoneskin efficient because of the time cost (3 seconds vs a 2.5 gcd of regen or cure I). The only benefit of stoneskin is, like others mentioned, it effectively raises the max HP of a player. Regen is MP efficient and Cure I is MP efficient. The proc you get from Cure I costs no mana. Sure that proc is hard to time, but if you're really blasting the tank with heals (spamming Cure I) you'll eventually get 1 that is well timed and it does help with MP. So for generic healing, just keep regen on tank and only cast Cure I if he drops to ~80% or below.
Another issue that hurts whms, is they often try to heal through curses/diseases. Ensuna those b****es and save yourself MP that way.
