UDP is an unthrottled, connection-less protocol. Usually UDP is used for streaming video or audio, high bandwidth applications where when bits are lost people would not notice. Essentially your computer just spits out data and "hopes" that it reaches it's destination. Because Torrenting/uTorrent in nature automatically ensure that all data is received, using UDP is not a problem. UDP will make better use of bandwidth because handshaking does not occur, thus less overhead. Also, in TCP it is possible that clients can tell other clients to "slow down" if they are outputting too much data for the network. Thus why TCP is said to be throttled. In UDP there is no throttling, all clients can output as much as data as they want, as fast as they want, into the network.