These are thumbnail sketches. I do these to work through ideas and compositions for some of my pieces - try to get a feel for what works, what's within my current skill set, etc. As a general rule, it's good to do a few mock-ups before you do your final work (they don't have to be super detailed - just enough to get a better idea of what you're doing) as it usually results in your final piece being that much better/more refined.
This set was the first stage in my recent Smoking Tiger submission.