Manufacturers put top weight in a ball to offset the 3 oz or so removed during drilling. By moving the cg away from the grip center the top weight can be converted to positive/negative side weight and/or finger/thumb weight. But in today's balls these imbalances have only a minimal affect on the ball's reaction, unless they are used to allow drilling of a balance hole which does affect the ball's reaction by modifying the core. After drilling, for the heavier ball weights, the USBC limits are 3 oz max of top/bottom weight, 1 oz max of positive/negative side weight, and 1 oz max of finger/thumb weight. -- JohnP