I don't think I've ever seen anyone use chains with pull ups/chin-up from a 'accommodating resistance' standpoint. Especially since chinups are harder as you go up.
Chains draped over you shoulders/neck isn't a bad option (or say a weighted vest) over a belt for weighted chins ....its a whole lot less swingy. Its a different center of gravity too.This gym has multiple weight suspension belts.
Also depends how high the bar is, etc. ...the step-up point/apparatus to initially grab the bar. Easier to get started, etc.
All this applies to dips as well. At my gym the plates will hit the ground on our dip bar set up.
More than likely, it was a look-cool thing.
To be fair, there is a little more complexity to using a weight suspension belt vs. just draping chains over one's self. If he's looking to add weight, it's moderately simpler to just throw those on, if they're already there. But yeah, it probably looks cooler in more general circles.
Good for him for doing weighted chins at all, I'd say.
Being of an older school, I'll admit that the initial Alice comment took me straight to Cooper. If I visited a gym and saw him there, doing weighted chins, now that'd be cool.
The very first one here is pretty egregious...the kid in the green shirt.
https://twitter.com/i/status/1731350404074520999
I believe this is the thing Rip was talking about how the trap bar CAN be unstable in the sagittal plane.
I mean first off, the kid can get the thing moving without his whole back collapsing,
BUT then he tries this explosive extension thing (like the other kids are doing) as the bar get up near the top,
and the COM of the bar-load gets way in front of his spine and hips.
It looks so weird, awkward, and dangerous.
Much performance.
So explosive.