There are plenty of free ways to use BitTorrent. Here are a few examples:
Open-source software, such as Linux distros, are often available for download via BitTorrent. This saves the organization maintaining the distro from having to host the files themselves.
Public domain media, like old movies, books, and music for which the copyrights have expired, can be found and legally downloaded through BitTorrent
Independent artists making movies, games, books, and music often post their content for free on BitTorrent.
BitTorrent is a convenient way to access fair use materials from various media