Our grill has cast iron grates. Unless my wife is there when I'm getting the grill ready, I don't "clean" them. If she is there, I gotta do the whole scrub-and-wash routine with them.
(She is MOST annoying about that and you absolutely CANNOT convince her otherwise. A case of "just do it to keep her happy", if ever there was one.)
Otherwise, the most I'll do is brush them down a bit with a wire brush, maybe wipe afterwards.
If you scrub the grates on ours the way my wife insists, stuff sticks to it. If you don't, they stay seasoned and stuff doesn't stick.
I'm a firm believer in fire making anything safe with respect to cooking on the grill. Any critters on the gratings are long dead and gone by the time I'm ready to throw the food on the grill.