I've done this before, but on Windows. There was a setting with an older version of iTunes on Windows where it would automatically manage your music, which mean

I've done this before, but on Windows. There was a setting with an older version of iTunes on Windows where it would automatically manage your music, which means that it moves it around and takes ownership of it. If you try to delete something from your itunes library, that you thought you copied, it would actually delete your music, not the link between itunes and your music.