A mouse pad is intended for use with different mouse options. If you use an optical mouse, however, a mouse pad isn’t always required. While a traditional mouse includes a rubber ball, an optical mouse has an optical sensor that detects when the mouse is moving on most surfaces. But if you use an optical mouse on a semi- or fully reflective surface, the mouse's optical sensor is unable to see which direction the mouse is moving. In this instance, a mouse pad is required to track the optical mouse's surface movement and direction.