...I have absolutely no idea, haha. First of all, I haven't figured out how to do that yet. I think it is mostly for show, but also maybe as a way to keep in rhythm. I've noticed that when I'm trying to play a complex or syncopated beat, I often find that I get antsy hands and either get off beat or mis a beat. Maybe the twirls keep that from happening? Or maybe when you are in the middle of laying down some awesome rhtyhms, you get caught up in the music and your hands just go with it.

I have never taken a drum lesson or even really talked to an actual drummer, so my opinion is worthless. I just bought a cheap set, and started teaching myself some basic stuff.