Time to 'Breed' life into the sketches ;)

I think there are two things sitting at the core of the sketching process: Iteration and speed. The whole point of producing multiple thumbnails in black and white (iteration) is basically to test the ideas you have and validate that idea before you commit lots of time to work on it.

Obviously, this sketching process is ideally something that you can do quickly so that you can test lots of variations and leave the bulk of the production time for the proper polished work.