It’s not only noise. For the whole flight you are trying to save as much fuel as possible and you can easily eat up the few kilos you saved during the flight by applying max reverse thrust.
Since reverse thrust isn’t even considered in the landing distance calculation (on dry runways) and max reverse doesn’t increase the lifetime of the engine, I can’t imagine that max reverse can be mandatory.
Furthermore from the cabin it’s impossible to tell how much reverse thrust is being used.