FIVE TYPES OF THUMBNAILS
by RON LEMEN
It's great insight on the process and utility of creating thumbnails for illustration. I recommend reading it to anybody who has trouble with composition or who have found themselves trying to figure to many things out along the process of creating a piece.
Lemen provides descriptions and usage explanations of five thumbnailing techniques, ranging from the very rough sketchy ones to the ones that contain late stage information for the piece.