Tossing the dough looks cool and gives people the idea that you're Italian. (I don't think I'd fool many with my looks.) Aside from that, it allows you
to enlarge the dough without "flattening" the cells in the dough with a rolling pin. We roll it out with a dough sheeter (mechanical rolling pin, really) and toss it the rest of the way. Tossing also helps you balance the crust, much like balancing a tire. The danger (and something I have to emphasize to new employees) is to not let it get too thin in the middle. Practice with a wet washcloth. The trick is not so much of a toss as a spin around the outstretched fingers of one hand (right hand if your right handed). Kind of hard to describe in words. Picture holding a basketball in your two hands with the left on top and the right on bottom. Twist the ball counterclockwise simultaneously (left to bottom, right to top) while lifting your hands in the air. (If you're left handed, reverse everything...right-top, left-bottom, clockwise, etc.)