There would be a function or tab that shows all of the places a song is stored in your library. In short: its impossible for me to track down every playlist a particular song is in for me to delete duplicates.
Let me explain. So this just bugged me more recently as my library is crowded with an abundance of songs that need sorted into playlists. Basically, I just noticed the same song in about 5 different playlists I had. Not a fan of repeating the same song throughout my library because I like to listen to a large diversity of songs. Anyways, it's impossible for me to track down every playlist a song belongs to for me to delete the duplicates.