If you’re referring to the hole in the top corner of a meat cleaver, that hole is there so butchers can hang the cleaver so that the knife is hung with the handle down versus the blade. I imagine they used to hang it by a lanyard in the handle until too many butchers walked too close to the cleaver and lost an ear.
If you’re referring to the divots that you see along with the blades in some butcher knives, those are there to create voids between the meat and the blade to prevent the meat from sticking while you slice.