They are an incredible inovation! You can set them up to set a particular figure's texture, bump and/or transparency maps, material group colors, morphs - in whatever combination you need. Once set up, you can organize them in library subfolders and apply them with a double-click. A good reset pose can set it all back to a neutral state. No more plodding through every material in the material editor once you've set up a MAT, or remembering where all the texture files for a character are. You can mix and match files located all over the place. It's a snap to try out various textures on a character, etc. More venders are providing them with their products. I can't guess how much time my initial investment in learning and organizing my MAT libraries has saved me. I just copied the MATs that came with Vicky2 and experimented with changes. It's basically a very small piece of the .cr2 text. (Have I raved enough to get you to try them?)