At Catalyst fitness last July I was doing arms on Thursday and found they had a Hammer Strength Bicep curl machine. My old gym had the same machine. It was funny to see a weight plate under the lower floor support arm. This raises the handle an inch or so the user doesn’t have to lower it as far down. I don’t know the exact reason you would do this – perhaps you have elbow issues and want to alleviate strain on them. Maybe you want to keep constant pressure on your biceps and this is how you do that. When I used the one at Spiece, there would always be a weight plate in the same place under the support arm on the floor.
I used to leave it there and now I remove it so my arm range is far as it can extend. Do you have a machine like this at your fitness center? Do you or others put a plate under it, too? It’s funny how both gyms do the same thing on this machine.