dual
I am dual clienting a mage and a shaman. While the mage is full of mana all the time, the shaman is always low on mana but that doesn't mean he always needs to be full of mana. Yes, the slow and the malise and the dot are really expensive (and at times, I don't even malisement and just malise with the mage), but while the mage is on top of things healing the pet and sprinkling in a nuke my shaman is in the back meditating. Sometimes a monster is hitting more often then I like it, so the shaman needs to help with the healing.
The healing is really expensive at 41 so I might get 2 or 3 off and just have a tiny bit to go for another. If the canni was implemented like a lich, I would have to wait for a tick but in this case, the shaman needs the mana now so he can start casting the heal sooner. Sometimes that is all it takes to win a fight, a few seconds shaved off in response to something.