Butch, actually, besides the photo realism, a complex scene the shadows can be used to highlight a piece of the image, increasing it's importance. like a face glowing in the shadows in a dimly lit booth in a bar, the glass/drink on the table a sugestion of reflections that hints at the rest of the figure. this effect draws the eye to the details in the shading of the shadows, which increases the apreciation for the complete complexity of the image.