Aside from arousal and experiments the few instances of voluntary self inflation have been for mobility reasons, like Avana offsetting extra weight to reach high shelves. Once Sara inflated herself with helium just enough to float at near neutral buoyancy just so she could take a nap while nearly weightless, a helium hammock if you will. Mya will occasionally do it as well just to make her boobs bigger and rounder to flaunt around because she's a boob gremlin like that.