Shortening servings will only cause a problem if you make them too short. Too often, they're much longer than need be. The amount needed varies with each archer. If you're shooting 3d with a release and never hit your sleeve, you only need enough so it doesn't move. Adding Brownell's serving lok can help. I also see a lot of end servings that are 2-4" longer than need be. They should be shorter if for nothing but cosmetic reasons.

And yes, shortening them will reduce weight. When you reduce weight, especially toward the middle of the string, the arrow goes faster. I'm not talking 20 fps, but a foot or two per second is very often added if someone has rediculously long servings. Besides, strings look much better with servings as short as they can be. One reason I don't like single cam bows with roller guards, is that the cables are practically completely covered with servings. They'd be prettier if you could see the string colors.

Same is true with reducing string weight by reducing strands. It does lighten the string and slightly increase speed. Same principle by using 8125 instead of a heavier material. Do I recommend this? No, I actually add strands if my cam groves can handle it.

I was including things that speed freaks can do to can that extra foot per second. Heck, you can lose a foot by waxing your string heavily and frequently, but I don't recommending not adding the wax. The biggest gains come from removing brass nocks, peep holders and ridgid loops.

I use to build strings differently and then crono them to see what would happen. You can even change speed slightly by building a string with very few twists. If you build a string a 1/2" too long and then put a lot of extra twists in it, to obtain the right length, it will slow the string a tiny bit. Most of these things, by themselves, means nothing. Add them all up, and there's a detectable difference.