Let's say I've downloaded big file using torrent. Then add very small file and recreate new torrent file. Like subtitle.
Now two torrent files are totally different file to machine. Tracker and torrent client would treat them different torrent. Of course we don't need duplicate original data file for multi seeding. But seeders and leechers split by two torrent file. They don't know about they have exact same file. Torrent client and tracker cannot connect people for exact same data. We have split share pool for exact same file. It's not efficient. More seeders, more speed.
Let's say original torrent file is 1.torrent.
[ file1 ]