I'm supposed to, but I have forgotten a couple of times, but no bad results, yet. As long as the reverse turn is not too sharp, it won't jam up. The friction bar can only get so short, and after that it would restrict the trailer, and probably bend or break, or break of the small balls mounted on the hitch or the frame.
Since it is located on the passenger side of the trailer coupling, it actually gets longer when I back up the trailer from the drivers side.(Imagine pulling past a camp site on the left, then backing up into it with the site on your left. But I suppose it could get trapped against the trailer frame if to severe?? Not sure as I haven't accidentally hit that limit yet. I finish backing in and get out to level the trailer and realize i haven't disconnected it.. Oh well..