If you run out of mana you probably don't understand that spamming heals accomplishes very little, versus well timed heals.
Also your probably afraid to let medica 2 tick people to full and cast too many medica 1s, when 99.9% of the time you know when the next aoe is coming (unless you don't pay attention and have low awareness of fights).
Even the first half of turn 9 I', just find myself spamming aeros and stone 2 in boredom attempting to not miss (and the miss % is crazy high), because all the damage is reliably timed, and I know I am going have full mana by the end of the first or second add phase.

Only thing more useless for a WHM is crit.