I've cast dissipation once, and only to see what it looked like.
I'm having a very difficult time finding circumstances that would justify using this skill in a combat scenario. It seems to lower healing output and cost mana. Completely ignoring the capstone spell of a job strikes me as fundamentally wrong.
But perhaps I'm looking at it wrong? Are there cases where I should be using it? What should my mentality be when using this ability? Let's talk about it.