Even on round comers or curved fenders, every square inch of paint must be made optically flat. If you were to inspect a car's paint surface under a microscope it would not look flat at all. In fact it would look rough and have the appearance of deep crevices and high mountaintops. These are what are called high peaks and low valleys in the paint. High peaks are mused by paint overspray, bird droppings, tree sap, surface calcium deposits and dirt.
Low valleys are pores containing dead oxidized material, sludge and dirt.
Just by looking at the surface with the naked eye, it is usually too difficult to tell just what degree of roughness from peaks and valleys are present. You can get a better feel for the condition of the vehicle's paint by running your hand across the Surface. Although you won't be able to tell everything by just running your fingers over the surface, a car that is well maintained should feel smooth, not dry. Generally, if the surface is not smooth or is hazy or dry, and doesn't bead water during the washing sequence, it is a sure candidate for polishing. To achieve a plane of an optically flat surface, like that of a mirror you must first abrade or cut the paint.