I'm thorn on this topic.

As a SCH, I hate that I will throw Excogitation at a tank when he is almost 50% HP and they panic, clicking every single cooldown, never ever getting to 50%HP and therefore never procing the 650 potency heal, wasting my Aetherflow.

As a WAR, I hate that Upheaval becomes worthless if my HP is not high enough, a skill I feel should be ideally always be kept on cooldown. Paladins also have a similar issue with Spirits Within.