Is there an optimum one light setup in terms of lighting the subject, providing fill (i.e through reflectors) and possibly lighting the background as well?
If you are armed with only one light, how would you produce the best result?
One clever way to get a good result from one light is to use the corner of a room/studio with white walls.
Place your subject in the corner with your light at a 45 degree angle to the corner.
The back wall will be lit by the main light, as well as reflected light off the other wall.
The far wall will reflect light back onto the subject to provide fill, and due to light falloff, will be dimmer than the main light. By moving or turning the subject you can achieve different light ratios. And the walls act like big soft lightboxes.
A starting point would be to have the key light off camera and a reflector providing fill as shown below. This would produce a good result, but would lack a hair or background light.
A variation would be split lighting - move the light almost 90 degrees to the subject. A reflector opposite could provide fill.