The waggle is an important part of the pre-shot routine. It’s very difficult to start a smooth golf swing from a stationary position and the waggle gets your energy flowing. It’s a way to get a better feel for the swing you are about to make.
While a pre-shot routine is just that: a routine, the waggle is used to simply start movement. But don’t incorporate a move in your waggle that you wouldn’t incorporate into a golf swing. It doesn’t really matter what kind of movement is generated, as long as it promotes good fundamentals to the golf swing.
A waggle before the swing isn’t totally necessary and there are some great players who don’t use one. But for many players of all skill levels it’s a good way to ease tension before a shot.