I have the new biscuit and can remember people recommending trimming the back side. I saw the diagram, but really can't figure out what/how to do it and what does it really do.

I am shooting feathers and have seen a little wear on the edges but flight is good.

Is there really anything better than a nicely trimmed biscuit?

trimming reduces friction which reduces fletching wear and increase speed. The new Biscuits trimming is not nearly as important or effective as on the older ones. Over trimming can result in decreased holding power so you need to be careful. Fat aluminums will tolerate more trimming while the skinny pultruded carbons really won't take any trimming before they start to "slip between the bristles" CAP has a diagram on there website, it's under the tuning for finger shooters section.

Speaking from experience?

I guess my answer would be: "It depends."

But as you know, I have never used the rest, and never will.