Ranger 75--Since you're not trapping the arrow nock between your fingers, as in split finger, the lower nock keeps the arrow from sliding down the string.
Also, if you butt your index finger against the nock, then draw to anchor, the increased string angle can cause undue upward pressure on the arrow nock. I found it could affect arrow flight for me at times.
By using 2 nock points I can keep my index finger 1/4" or so below, that way when the string angle increases near anchor I get no pinching on the nock.
I use 2 adjustable tied-on nock points. There are good directions for them in the How-To forum.