Why do you have to remove car wax before reapplying?

Question

and how often should you wax, and is clay baring worth it

Answer 1

It only needs a thin coating of wax, so you wax-on, wax-off, you are really leaving some wax on the car.  Clay bar is worth it if you want the finish to look the best it can.  If after washing the car you can drag your finger across the paint and feel bumps then clay bar or buffing in needed.  A new paint job will be smooth, microscopic junk on the paint builds up over time and you can actually feel it when it is on thick enough.  This prevents the mirror like reflection of a new paint job, so a clay bar or buffing will remove the junk and help it reflect properly.