Conventionally when you download a file it’s sent to you from a single computer. Depending on the size of the file and the number of downloaders this can put a massive strain on the transmitting computer and costs can escalate pretty rapidly. A torrent however doesn’t rely on one computer. When a user downloads a file using the torrent protocol they’re actually downloading parts of the same file from multiple computers. Every computer in this network are both uploading and downloading. There is no cost for hosting files and download speeds are practically unlimited.
Take a look at this example (Paddle Over) of the technology which ties social networking into file sharing (anyone remember Grouper?). Cool idea, eh?