Not an expert here, but I think wax fills the pores of the car which will help keep dirt out of the paint. Wax also puts a thin layer of protection on the paint to protect against corrosion from water, salt, etc. Wax makes the car easier to clean off and shiny, too. You will be suprised when you wax a small area, just glide the cloth over that area. Then glide it over an area you have not waxed yet. The area you waxed will feel a LOT smoother and the cloth will glide right over it, where the unwaxed area will grip the cloth more. But I think the main reason for it, to me, is the protection it provides to the paint. It is not difficult to apply, it's just time consuming. I know I will take a beating for saying this, but I use Turtle wax, the stuff that's $3-$4 for a can of it. The reason I do this is because it's what my dad uses and his 1994 Dodge Dakota looks brand new and he hasn't even waxed it for a couple of years because he was sick.