"..The planes of the head should be memorized, for through them we have a foundation for rendering the head in light and shadow..." (A.Loomis)
Working on these magazine photos I was surprised to see how smooth were faces. Almost no visible planes. Loomis actually writes about it:
"...If you have softened the edge so much as to have lost the plane, the drawing is bound to take a smooth, photographic look. For this reason, planes have to be established when you are drawing from a photograph, since they are not apparent..."