With the current very low gear levels and people learning the fights the last bosses of Neverreap and Fractal can be MP nightmares. I've used dissipation on 3 separate occasions to avoid a wipe.

Is it situational? Yes. Are there very few situations where it is useful? Yes. Can it save you from a wipe sometimes? Absolutely.

From the XXI live letter: "Instead of just simply increasing a scholar's abilities, we made adjustments by adding actions that require you to really think about their use and the best time to utilize them."

The fairy sacrifice is the trade-off. If you use it at a bad time you are hosing yourself, however at other times you can be the hero (which only you will know because nobody else even watches the hp bars). The fact that it isn't an overpowered no-brainer use it on CD ability is exactly what they were looking for, and they nailed it.