They are supposed to help with balance, noise and overall handshock when firing the bow. There are tons of different styles and lengths to choose from. If your using it for hunting, id recommend a shorter one since they are alot easier to meaneuver in the woods. I have a 4 inch carbon express that does the job well. My next bow will have one of the new Octane piston style ones on it, they seem sweet. Good Luck.