Why concept cars? For obvious reasons - to get a visible, tangible look at a design before production so its feel can be evaluated, possible problems can be foreseen, and, for concept cars shown to the public, so reactions of non-gear heads can be judged.
In testing particular ideas, concepts are best - for example, they could be a test bed for exterior and interior colors and materials, new controls and dashboard layouts, variations on packaging, etc.Driving concept cars is a wonderful experien.