 So, you have absolutely no clue why there's an option to do nothing, not a problem. This confused me a lot when I started too, but doing nothing is actually quite useful. Remember, all three modes for face edges and points are on at the same time. So let's say at the moment you're just trying to change the polygroup colors of a bunch of faces one at a time, and you're trying to work fast, but sometimes you accidentally click on an edge, or you accidentally click on a point, and you end up doing things you really didn't want to. Well, this is an ideal situation which you would want to set points and edges to do nothing. If you set points and edges to do nothing, you'll never accidentally click them. That's what this option is for, so you don't accidentally click points and do something you don't want to. Hope that helps, and as always I hope you have a fantastic day, and I'll see you around.