lobi:

In my experience with the Biscuit, the point of impact does not change when you trim it, as long as it was set up properly in the first place, and the position of the Biscuit does not change. I have noticed that if the rest is not aligned with the bow string (perpendicular to the arrow) then it will have the effect of making the arrow shoot lower or higher, especially with broadheads. If the rest is angled somewhat, then trimming the biscuit will have less of an effect of pulling the arrow up or down. I personally would not mess around with it in mid season, unless you are really not satisfied with the way it is shooting. I have had too many times when I was adjusting this or that a day or two before I went hunting. Some of those situations cost me deer, fortunately the worst that happened were clean misses and a superficial muscle wound to the chest of one deer when I shot low.

IMO, these rests are not as easy to set up correctly as some people think. If you take the time to get them dialed in - nock height/rest height, center shot, Biscuit angled properly, etc., the accuracy you can get from them is very close to, or in some cases equal to what you can get from good shoot-throughs or drop-aways.
My broadhead flight and accuracy is equal to or better than any other setup I have ever shot, and the arrow can' t possibly be in the wrong position for a shot. After years of shooting a Centerest Flipper and Plungerest Low Profile with a rubber band arrow holder, I am totally at ease with my setup.