ahh but if your scene was lit correctly then no objects would be complely dark.... j/k I can see why you would use it. Dont you find that it pushes your render times up too much though? I hate to say it but if you want to make sure that everything has at least a little bit of light then you could use an ambient light at a very low intensity.
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB