Overhealing is a waste of mana, The definition of overhealing is every point of healing done that goes past the Tank's maximum hit points. Now assuming every single decent priest spamming flash heals is also using mana conserve, almost every single crit heal is simply a waste, it either overheals or causes the next person's heal to overheal instead thus in almost every situation is not worth the trouble of getting.

Seeing as the job of a priest is keeping the tank at maximum HP all the time so that he has the maximum chance of surviving burst damage at all times it's actually basic logic that Crit healing is indeed close to worthless. Why ?

The only way to use it in a way that does not cause overhealing 90% of the time is that you heal when the tank is on substantially lower hp then the healing caused by your flash heal, I.E your Flash Heal heals for 1000 so you never heal unless that tank has lost 1500 or more HP, this is not smart or efficient as this works against the priests main job of keeping the tank at maxed out HP and is based purely on luck.

It's not dependable, why ? Crit heal does increase your healing yes that is true but when ? Only when you're lucky that's when, even with 50% crit chance on spells wich is impossible to get you can easily cast 10 spells that never crit or go 10 spells in a row that crit all of wich heal for more hp then the tank had lost.

In conclusion, it is my oppinion based on my own and other people's experience that crit healing is only useful for increasing your standing on the “Healing Meters” wich is what fools many into beliving that it is actually useful, seeing as the Damage Meters mod has no way of seeing what is overhealing and what is not.