The coating is not always desirable. The coating keeps the ink from being absorbed by the underlying fibers. This is called holdout. Since the ink remains on the surface, it can be more vibrant and detailed. Paper that absorbs the ink will blur the resulting image, producing poor colors and dull images.
Coatings can also hide flaws in the base sheet.
Some low-rated coated papers have groundwood content. Cover is usually heavier stock. It can have a matching bond, text, or book sheet. The maximum reflectivity would be one hundred percent. Brightness must be selected based upon the application.