I wonder how often a bit exact copy of one song appears... Sure the songs might have the same title and duration, but some very trivial edits might be done. You need to be extra careful when identifying these songs as identical if you don't want to lose any information.

Of course, from a listener point of view it might not mean much, but how would you decide at which level of non-similarity a track is the same as another one?

It's a bit like choosing a lossy codec quality, it's very subjective, and for indexation this might not be the best way.