When is it effective to "block in" an area?
I found it better to create large totally black areas in parts of this illustration. The reason for this was the high amount of complex textures in the photo. Too much information tires the eye and creates an overall busy appearance. Dropping out some areas like the shadow on the neck was a good idea here. However, the hair still has diagonal shards of white that I left intentionally to break up this shape.
Why the two different approaches?
The mass of the hair was too large a shape to simply render in solid black. Plus, the hair needs to appear light and "frizzy" as it is in the photo. My solution was to give the whole image more dynamic thrust by leaving diagonal areas of white in the hair and on darker shadow portions of the body, as well as the background. This becomes a unifying stylistic theme that pulls the whole illustration together. The verticality of these strokes makes the figure look more animated, always a good quality when trying to create a lifelike portrait.