Warning: From a 1 year novice.
I have 5 pins and I plan to use 4 this year. I have one from 25 yards in, then one at 30, 35 and 40. I am accurate out to 40 yards, and I found that with my bow the arrow drop over 10 yards was enough (4-5 inches) that it made sense to have them at 5 yard increments, that way I will be able to aim dead center at any yardage out to 40.