Suppose for climbing/rappeling down the team uses ice screws to make the base. Obviously the screw will need to be recovered after everyone has gotten down.
We were taught and shown (and I have forgotten, hence the question) a nice technique to tie a cord to the ice screw and let it rotate around the screw as it (the screw) was being driven into the ice. Then tugging on this cord from below would unscrew the piton from the ice. Basically this would allow the climbers to retrieve the ice screw after the last person got down.
Of course, using a V thread to make the base to rappel down circumvents this problem. But I would be happy to see a video or read a short description of how to recover the ice screw.