Holding up pants. This is the most obvious use of a belt. A belt can help to keep your pants from falling down, especially if they are loose-fitting or if you have lost or gained weight recently.
Accentuating the waist. A belt can help to define the waistline and create a more flattering silhouette. This is especially important if you are wearing clothes that are loose-fitting or that do not have a defined waistline.