3 Point lighting considerations
Portrait photography lighting tips. ProPhotography 101.
http://www.epl.org/library/strategic-plan-00.html (accessed August 8, 2012).

Hair light

The purpose of the hair light is to help separate the subject from the background and to add a little bit of dimension

A light coming from above (and slightly behind) the subject will add a little roundness to the shoulders of the subject and lighten the upper edge of the subject too.

This light is especially helpful in separating dark hair from a dark background. If the subject is dark and the photographer wishes to keep the background dark, this edge light will tend to brighten just the hair and shoulders, separating, but not overly brightening the subject

If the subject is follicly impaired (bald), you might want to turn this light completely off.

Subject's weight
These two images were shot under the same lighting . Notice how the body is lit in one of the frames and not in the other. This is a tool to be used. In which photo does the subject look to be thinner? Just something to kick around...