Couger, here is the idea. I'm by no means the authority or know all on this, but I can tell you my expereinces and what I learned from some very knowledgable people.

Binary cam bows are very cable sensitive. If you setup a fall away to stay up for as long as possible to guide the arrow, which most shooters recommend, it will pull quite a bit on that cable at full draw and actually create a "shortening" effect. So in you have to take a twist or two out of that cable to keep your cams in synch. What everyone found was that if you didn't do this, you actually lose let off because the cam is retarded slightly from the top cam.

Hope this makes sense.