Since even before Traktor I've wanted an undo feature, it's so obvious but yet its not there and it would be SO useful.
Just a couple examples.
You load a track into the track that's playing, instant fix, probably would sound cool as well.
Utility stuff like you drag a track to the deck but miss and put it in the playlist instead, now you don't know where it was!
Or just deleting stuff by mistake in the playlists, TOO many situations that it would be SO useful for and probably some creative ones as well.
