The first thing to notice is that the difference in launch speed between a 24 oz. bat and a 32 oz. Because a baseball bat has to have a certain diameter, and has to be made of solid wood, it turns out that after a certain point the only way to make a bat lighter is to make it shorter. Hence a 24-oz. In the development of tennis racquets the real breakthrough came with the introduction of construction materials other than wood. Originally, aluminum bats were introduced simply as a money saving device.
Aluminum bats are virtually indestructible.
In addition to their longevity, however, aluminum bats have some interesting properties. Since they are hollow, their mass distribution is much more open to adjustment. The overall shape can be changed subtly but the mass can be held constant simply by adjusting the wall thickness. In particular, the taper to the handle can be delayed, producing a bat with a barrel diameter which stays large closer to the handle. This produces a larger sweet spot, and a sweet spot that extends further toward the handle.