Is there a special name for a type of spin in the air where the person's body is almost horizontal? I have seen it in several action scenes, such as this fight scene from a movie (at 1:41). Ninja Assassin Fight Scene
This looks like the wushu butterfly twist. It's more gymnastic than useful for fighting.
As per mattm, it's the "butterfly twist" in Wushu. In Capoeira, it's the mariposa (which also means "butterfly" in Spanish, but in Portuguese more often translates to "moth" or "prostitute") and my copy of Unknown Capoeira: Secret Techniques of the Original Brazilian Martial Art notes that it is indeed ornamental, although, as with many spins, lashing your foot out in the midst of it can transform that spinning momentum into a strike, and of course it does work as a dodge, albeit one that's more flashy than utilitarian. Lastly, as with most acrobatic moves, it sometimes can just be intimidating, since it shows your body control and that you're confident enough to waste energy on something flashy.