1-light & 3-point lighting against daylight in an office
Here they have a typical scene set in an office with our main subject sitting at a desk. The lighting in this scene can certainly be improved by balancing the light on the subject with that of the background.
This time they take a more traditional approach with a key light, fill light and back light as well.
The reason for working with 3 lights, as opposed to one, is that this gives use greater control over the lighting and the ability to create 3D modeling in a 2 dimensional space - in other words, to add shape to your subject through light.
Text and video via Dedo Weigert Film GmbH