I look at people when talking, but partly becasue I'm also legally blind, I really have never figured out how to use it, but I know it's used for the reasons above. I developed a very good eye roll - though I'd never used it before - when I became an attorney specifically for use with clients who did or said dumb things in civil cases. I was nice and never used it on the opposition, but I found it a good way to show how maddening one in particular was. (The use of such nonverbal cues may have been why I felt such overload and eventually dropped any and all trial work.)
It is also a good way to show anger. When I was in my early 20s, my cousin, who was 6-7 at the time, taught me how to do an angry glare when I asked him, since I'd seen it in the funnies but never could figure out how to do it.
Which shows how accepting kids are at times - he didn't seem to find it odd at all that I hadn't developed that on my own.