But did you also know it could also be used to fix corrupt files you've downloaded?
Say, for instance, you've downloaded the latest ubuntu.iso directly from your browser. You had problems trying to use, so you've checked its MD5 and it didn't matched, so you know your file is corrupt, but you would like to avoid re-downloading 700Mb again.
All you have to do is download the correspondant .torrent file, open with your preferred bittorrent client (Transmission, uTorrent, Vuze, etc.) and, when asked the location for saving the file, indicate the folder containing the corrupt .iso file you want to fix.
(Most bittorrent clients will do this automatically, but it might be necessary to ask for a manual verification of the "local data" to assure the application recognizes the file you want to fix.)
Bittorrent will adjust as needed the file originally downloaded, getting from seeders all the missing parts and, as the case may be, by deleting extra/corrupt bits of the file, so that your file becomes exactly the same as the original, good one.