I think the chamfer matches up with the shape at the bottom of the hole, but not sure. The reason would be to give more "bearing" surface area so it's less load per square inch. But in reality, @eaglescan is right, the shaft isn't going to jump out of there; however, somebody at Rotax thought it was a good idea to use a clip since the Funduro. If you broke the clutch arm at the cable, I guess the shaft could come out but you are screwed at that point anyway. As for taking too much off, after you take your cable loose, you should be able to feel how much "slop" you have up and down and give you an idea how it should fit after you grind. I don't think it would matter if it was a little more loose. Just make sure the clip is firmly seated, the real downside would be the clip coming off and start bouncing around in there. They are called Jesus clips, because when one springs off the shaft while you are prying it, and it goes shooting across the garage, you say "Jesus, where the F*** did that thing go!"