But Wait - Bat Weight is not as important as "Swing Weight" (moment-of-inertia)!
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There is a big problem with the discussion of bat weight that I have summarized in this article. All of the physics used to derive the optimum mass and the batted ball speed assume that the ball hits the bat at its center-of-mass. This very rarely happens - hits at the sweet spot are several inches from the center-of-mass. There is another very important parameter of the bat which affects how quickly you can swing a bat, and what the final ball speed is. This parameter involves the distribution of mass along the length of the bat and how that mass distribution affects the motion of a rotating object. In physics we refer to this parameter as the moment of inertia. It turns out that the moment-of-inertia (or "swing weight") matters more than mass..