All latex paint is designed to be applied in two coats, the "prime coat" and the "seal coat" A brush or roller must be used along with the sprayer to force the paint into the material and create a smooth, sound surface for the final coat. It also levels the paint, showing the true paint color. Just spraying causes the paint to dry as a film on top of the material, with very little bond to the surface. Look at the extreme difference between just spraying a surface and back rolling the surface immediately after sprayed.