I was wondering this myself a while back and decided to try a pendulum sight. I quickly went back to a fixed three pin sight. The pendulum sight was noisy and judging distance is bad enough with out having to judge how much to hold over the spot you want to hit. I sighted in at 25 yards and did not find that I would hit dead on out to 30 yards. My arrow still droped a few inches just like it did on the ground.

I just didn't see the point.