"Moons, cleanse the lands!" - Fina
While not as powerful as Aika's Super Moves, Lunar Winds is a useful technique, due to its unique effect. Several bosses (especially the optional Game Cube-exclusive bosses) have moves that bestow status buffs, thus being able to remove them can make the battle easier. Of course there's nothing to stop the boss from attempting to bestow the buff(s) on themselves again later, though one can argue that would be better than having them use a powerful Super Move against the party instead.
In random encounters, Lunar Winds is not as useful as most enemies are easy enough to deal with, even with status buffs.