Kent,
What does one use all those different matcaps for? Is there some sort of video on that subject?
Just the sheer number of them seems like they all have specific uses. One even seems to represent a normal map...
They're just there for visualization purposes within the viewport. It's a cheap way to get fake reflectivity and shading with a simple texture. Though you can render matcaps with a node-setup: https://blenderartists.org/forum/showthread.php?303899-SOLVED-matcap-in-cycles-with-nodes
