No matter how clean your paint looks, there are almost always contaminants such as industrial fallout, road tar, dirt and metal particles embedded or trapped in your clear coat and beneath the surface of your paint. By running your hand along a clean paint surface, these contaminants can be felt as bumps or imperfections. In the case of metal particles, these tiny fragments can lead to rust contamination if left over prolonged periods of time. In order to properly clean and protect your paint, you need to first remove these contaminants in order to give your paint a clean and smooth surface.
Clay is not a replacement for polishing compounds but rather a malleable clay-like plastic that removes contaminants by shearing them away from the paint and enveloping them inside the clay bar material where it is prevented from doing any further damage to the paint. Properly used, a clay bar will leave behind an ultra smooth and slick paint surface that can allow paint protection products such as wax to better adhere to the paint, which in turn can improve their durability and ability to protect.