When I used to backpack in the White Mtn NF in NH there was always a discussion among the rangers about where to set up camp. Some felt that if you chose a new site every time the old sites had a chance to recover, and of course the other argument was using existing sites prevented new sites from being cleared. Either way was fine with the rangers legally as long as you were 1/4 mile from a road, and 200 ft away from a stream, river or lake. I preferred existing sites only because the were already cleared with a fire pit.