More sponge = more speed/spin, but more difficult to control
So it is common for most beginners or children to start off with a thinner sponge rubber, so they can focus more on control and let the body generate the spin/speed. Than oppose to using a rubber that is too fast for they skill and generating tons of speed and spin, but with no control and consistency.
Control also refers to how easy you can feel the ball. But all this also ties with technique and skills