It's easy to explore variations in lighting, too. By moving the light from one side to the other, I can completely change the value organization and the way the elements read. I can also discover cast shadows that I never would have imagined.
I start by trying to match my sketch, and then I look for ways to improve on it, as in the case of this illustration of a Teratophoneus attacking a fallen Gryposaurus for Scientific American Magazine.
I do the first two sketches out of my imagination, then do the third one after looking at the maquettes. The shadow side dark predator frames the light head of the prey.
I can also fine tune the lighting on a given element.
It's important to be open to any possibility that makes for a better picture. And in the case of a physical maquette, those possibilities often arrive completely unexpectedly.
To get the full, detailed presentation on video, check out my Gumroad tutorial: How I Paint Dinosaurs.