I use the clay bar twice a year. It takes all the surface contaminants off. Run your fingers over the paint before and after and you’ll see how smooth it is after. Tree sap is bad though so may need to start with a solvent or tar remover, then clay bar. I then machine polish with a swirl remover or light polish, then poly sealer or glaze, and hand wax. Twice a year. Stuff will tend to not stick to the paint then and car wash will usually do the trick. Then there are detailed and chain saws in extreme cases or a garage.