These are usually images that a director(usually for a 30 second commercial) will ask for in order to help him communicate with the DP(Director of Photography.) They’re meant primarily for solving compositional problems, and maybe color.  Any client who expects finished paintings for these types of images needs to either have a really good budget or a really generous timeline.  If neither of those two things exist, I don’t take the job.  These days, this is the sort of work for younger men.