Tor: Why should I avoid torrenting over Tor?

Short answer

Torrent clients can ignore proxy settings or announce an ordinary IP address through tracker requests, defeating the privacy you expected. Torrent traffic can also consume substantial shared Tor capacity and slow the network for others. The Tor Project explicitly advises against BitTorrent over Tor. Use a tool designed for your lawful file-sharing needs and assess its privacy properties separately.

Sources

Tor Project: Tor Browser best practices.