I have used 1 pin for the past 5 years. I liked the simplicity if it and had it set at 20 yards (figured that would be the distance i'd be shooting at).
As i understatnd it, (for most bows) the 20 yard pin will be dead on at 10 yards (the way the arrow flies). I did practice some at 30 yards and could get withing 8" or so, but probably wouldn't have evere shot at that distance. At shorter distances (15 yds)
With all that said I think I will be putting at least 3 pins on my new bow (15, 20, 30 yards) to take away some of the guess work.