I think you should be able to delete demos in-game, a command like /dlastdemo or something like that should work just fine. It would delete the last demo recorded just in case you didn't like it or if there was nothing interesting you liked in that previous map. It should help so that your folder doesn't get filled up with demos that you don't like, ect. It also would be very helpful if your making a movie, you don't have to look through all those boring ol' demos that have no interesting kills, ect. because you could just delete it in-game after it's finished recording if you didn't like it. I don't know, I just thought of this a while ago as I'm looking over some of my demos I thought it would be a good idea. :p