P.S. I haven't seen it in a single place I went to (even the places that have studs). I do see the need for it at times, but for very specific horses.
I actually do own a chain. I have a very high-strung gelding that absolutely and utterly went nuts if put in cross ties and *I* was not standing there. Had to be me, not my trainer, not anyone else, had to be ME and since his response to me leaving was to back up until he hit the ends of the cross ties and then start rearing, my trainer wanted to end that nonsense and make it darn clear that even if I left and the boogeyman is standing there, rearing in the cross ties would absolutely NOT be tolerated. She used the chain so if his feet started leaving the ground she could quickly yank him back down and make it darn clear that he was to keep 4 feet firmly on the ground. Serious safety issue and she wanted to end it fast. We left the chain on his halter for a while but never needed to use it after that so it's yet another dust collector hanging in the barn.
I've used a whip when leading my horse.... I didn't actually *whip* him with it though. He started invading my space, I tapped his shoulder with it so he moved back over where he belonged. He started to charge ahead of me, I tapped his chest so he once again moved back where he belonged. I've done the same thing with the knotted end of his lead rope, a reminder of "hey, this is MY space and you don't belong in it".
A horse charging a person though? Going to get whacked with whatever happens to be handy. Never laughed so hard as when my horse got beaned square in the butt with a cone. He literally stopped dead in his tracks "OMG, I can't believe you just did that, you hit ME with a cone! You really beaned my special lil butt with a CONE!". I saw my trainer whip off her jacket and become large, scary person with big, scary, flappy jacket when someone else's horse tried charging her and there were no throwable objects handy. Her goal was to hold her ground and drive the horse off to let it know SHE is in-charge, not them.