Finishes rarely look or “feel” right if left right off the brush or spray gun. Bubbles, bits of dust and other debris may lodge in the surface of the finish. You can feel these with your hand as you pass it over the surface. Brush marks and patterns from spray application will leave an irregular surface which is noticeable, particularly on gloss finishes. Rubbing out a finish is the last step in finishing and the object is to remove imperfections, even out and smooth the surface, and establish a consistent sheen to the finish.