Actually you should be using it at least once every fight. During the last few % it's essentially three free stacks to push out more DPS.

Aside from that, it has very niche uses. I can recollect quite a few moments where I've had to dissipate to save someone from a certain death. I think in most scenarios keeping a party member alive is worth more than the drawbacks of not having a Faerie for 30s. It's incredibly niche and should be reworked, but there are still uses for it as it is now if you actually try.