Primer spray paint is one of the most important aspects of automotive painting. It's ideal for touch-up and full-body paint jobs. Before you apply the color or topcoat that everyone sees, it needs a good paint foundation. After you've sanded the surface down real smooth, a good primer can help any paint color you apply to adhere to metal properly. Also, if you plan to add several coats of color or to provide some custom color, the right primer base ensures optimal results.