The "three light setup" is the foundation of all professional lighting. Nearly every shot you see in TV or in the movies, uses--at some level--the basic principle of the three light setup.

Here's why: television is 2-dimensional. People are 3-dimensional. The goal of the 3-light setup is to make people look more three dimensional on television and film. So the three light setup is a way of sculpting the human face to make it more natural and appealing for television (or movies).