I've been discovering lately how I can use the different values, or keys, to compose a good drawing. The relationships between darks and lights play an important part in adding drama, interest, and focus into the drawing. When one looks at a drawing the eyes are drawn to the place where there is most contrast, or most darks. In this drawing of a little girl the eyes are drawn darkest because they are the focal point and what the drawing is about.
There is so much more aspects about values which is important to painting and drawing, this thought dose not come by itself. I'd better stop here before I start trying to write down every though that comes from this. I don't want to end up over explaining and becoming totally inaccurate!