>>385006794
matcaps have a wide variety of uses, but essentially they can be used as "fake" versions of specular, rimlight/fresnel, metallics, and a whole host of other effects. but they are inherently inferior to their "real" counterparts. they are easier to set up and a bit more reliable across worlds but don't look anywhere near as accurate and have issues when looking directly up/down.
if you're using matcap as a replacement for specular and now switching to "real" specular, you can just drop matcaps altogether.