I would have to agree with lindsie here.
Sometimes, the only way to save the day is to spam PoH until your fingers turn green. It's a horrible situation to be in, but when the entire raid is on the verge of death and ... keep ... on ... taking ... ridiculous... raid damage... then renew blankets will not save the day, and PoH will at best delay the inevitable demise.
Those situations seem to happen a lot in my guild lately. Looking at other videos, it rarely happen that the entire raid take 20k damage every five seconds, but that's quite normal in my runs. Most of the time it's someone fscking up. Like when you get 4 slimes active on rotface, blood princes vortex clustering, or the meleers on blood queen failing to move out of purple fire. But the damage is there, and unless I heal it up, we're going to wipe for a week.
I feel bad having a third of my healing done happen through PoH, but it's the only thing keeping us alive; the druid (who is awesome) just can't keep the raid stable alone when the damage is that hight. So - manapool be damned, I have potions, dark runes, arcane torrent, H&H+sfiend and a sick amount of intellect. Notably no innervates or good manaregen trinkets. It's so easy to turn bitter ^^