Sleep related white mage question.

[aerolol]

Sleep is a good way for WHM to mitigate damage, but I honestly feel like it's not needed 99% of the time, and it just makes the run take longer. If your tank can hold aggro, and utilize his cooldowns, then the better option is to just let the DPS AoE and burn the mob. The faster they kill the group, the less overall damage the tank would take, and MP wouldn't be an issue.

^
This.
As a tank, I don't care about Fluid Aura at all. After a few seconds mob will come back to me anyway.
But I HATE BLM/WHM who sleeps mobs.
Maybe some really bad PLD need it because they have aggro control issues, but any semi-decent WAR or PLD doesn't need sleep/repose on mobs.
It only makes dungeons last longer and become more boring.

I'm a healer too (WHM/SCH) and there is absolutely no dungeon where sleep is needed or that I have been any close to running out of MP.

If a healer needs sleep so he/she doesn't run out of MP, this healer is doing something wrong.