Originally Posted by
Shenkz
They don't, that's why there is a talent to give you a choice, however if you've seen methods mythic HFC kill videos, from their Rdruid Sonies point of view, you can see him and their healers understand efficiency. With or without the wrath talent he will cast wrath anyways just to save mana during downtime, because it's free, but he talents it so he is healing and dpsing at the same time, for free.
They understand to let the paladin and priest spend mana during the spot heal portions of the fight and then let the druid and shaman drain mana during aoe healing phases.
Your average lfr player or normal/heroic pugger healer will just try to win the meters by overhealing, which actually doesn't count towards your healing at all, you will always get more hps by having the mana to spend on the big spells during high damage. If you can limit your overhealing to 10-20% while maintaining high total healing, you are ready for the big leagues.