Alot...If my brace ht, moves by 1 or 2 twists from the string on certain bows i have, there is NOTICABLE difference in arrow flight, A couple of twists will move your nock pt. up and down. Arrows will come out of the bow wrong, it can be a disaster. I usually start with the recomendation, Shoot 6 arrows.. Take notes, Move 5 twists shoot 6..Take notes..Move 5 twists, shoot 6 take notes etc. I usually go 25 to 30 twists in BOTH directions and figure out from there what worked best.. I'm happy when I can see my feather spinning down range with NO tail whip or porpoising. with a quiet bow. usually from there a bareshaft will fly well. If I'm prepared I'll use a video camera and tripod to review what I cant see. It takes a good couple of hours to get it right where I want it. Once it's set I buy a NEW "T" square for that bow and Mark it with a sharpie where everyhing is THEN I write it all in a little note book I have for that bow.