To me it is common sense and courtesy to remove the plates from the bar after you have used them. It would be so much more convenient if someone else wants to use the bar elsewhere. Imagine the bar with 200kg worth of plates on it and it's sitting in the squat rack and I want to use the bar for deadlift. I'm going to have to remove all the plates before I can even take the bar down. Re-rack all the plates after using. Don't assume the person after you will be using the same weights. I don't see how this is so hard to understand.