If you happen to move a thread, it is a nice courtesy to leave a "Moved" topic behind. However, I think you can safely delete these (not move to Dead Pile) after a couple of days so they don't clutter up the boards.
If you have to moderate a thread and move part of it to the Dead Pile, please leave a note on the thread in the Dead Pile so that those who want to can see why it was moderated.