When I kept cage birds I did allow them to fly around the room while cleaing out their cages, ensuring all windows were firmly shut, of course.
I believe that birds that are kept in relatively small spaces need to exercise their wings and use their facility to fly. It is not a problem in an aviary where they have sufficient space, but a cage does not allow the freedom to fly.
I do know someone who keeps the birdcage open all time in a closed room. Her budgies fly into the cage to feed, but otherwise are allowed to fly around the room. However I would not want that amount of bird droppings in my own room. An hour or so of regular exercise is more manageable, and the birds are always happy to get back into their cages to feed.
