TorrentFreak.com, admittedly a slightly biased source, has a good article on the benefits of BitTorrent distribution for indie films. Similar to arguments for online (or perhaps pirated) distribution of indie artists: The more people who see/hear your work, the better.
It’s interesting to think about how this affects the marketplace, but for indie producers with no distribution deal and a small budget for advertising, it could be a valuable part of the toolbox.