Some have stopped using the expander balls due to increased chance of pulling the neck off center, and less working of the brass. If your die allows you to "float" the expander ball, this may be minimized. Bushing dies allow adjustment for differing makes (thickness) of brass. Especially useful in 308, and may also improve the concentrically of the finished round. Especially if used in conjunction with a good comp seater.
If you want to deprime but not expand the neck, you can just buy the next size down expanding ball, depending on your make/construction of die.
Is all this necessary? That depends on your own specific purpose/reloading technique. Lots of ways to skin a cat.