They, IMHO, idiots, "stipple" their guns with them. I've only seen a couple in real life, but both of them looked very amateurish, to put it mildly. One of them had about 100 little conical impressions on each side, and I thought when I held it, "What is the point of this? The stock grip (It was an M&P)is rough enough."
Here you can watch a guy ruin his gun. Just my opinion, he seems happy with it. I just don't get the obsession some people have with an almost crazy fear of "losing my grip" on a gun.
YouTube