In most gyms I’ve belonged to, just about none of the serious guys put collars on the olympic bar - for bench, squat, deadlift, at least. Nor do I. I tend to do it on the E-Z bar, especially if it’s going over my head, because it is less stable. I’ve never come close to having a problem with plates falling off an oyl bar. I’ve even been to places where you had to bring your own collars if you wanted them, or buy some from reception.
[I say “collars”, but would prefer spring clips any day.]
Of course, I’d prefer anyone who is new to use collars, if they might fail to balance the bar. Especially if they’re nearby me.
But occasionally you see someone who clearly knows what they are doing, who takes the time to use the collars/clips. It makes me wonder why. It’s just second or two’s effort, of course: does anyone have any horror stories to share about events which have changed their outlook on this?
Of course, my favourite bizarre sight is seeing someone use collars on the kind of Smith machine where the bar is fixed parallel to the floor … if there’s a danger of those plates falling off, that’s going to be the least of your worries :-).