I was using them for performance really. The volume wasn't huge. I'd do three sets plus warm ups as a prelude to deadlifts. On squat days I did the same for cleans.
I got better at the exercises, and I think they kind of helped, especially deadlifts. But no real trap development. I only started seeing trap development when I started doing a lot more rows, and then it really took off when I added in pull aparts.
Deadlifts, which I've always done a bunch of, don't seem to do much for my traps either. Could be because I rarely go above three reps.