Pitchers will move around the rubber for various reasons. One reason is to increase the angle for which the pitch is delivered to home. For instance, the farther a left-handed pitchers goes to the left of the rubber, the greater the angle this will appear to a right-handed batter. Some pitchers like Satchel Paige were said to move all over the pitching rubber during a game under the believe that these slight angles gave them advantages.
More conventional baseball pitching focuses more on a perfected motion and keys into what Roger mentioned in his post: essentially, choose one good spot on the rubber and stick with it. Ultimately, you will have to decide for yourself which you feel most comfortable with. Feel free to experiment with this a little bit. If you feel like moving around gives you an edge, keep doing it. However, if not, just discard it. Since this the summer, this is a great time to do some tinkering with your pitching before the high school season rolls around next spring.