> It's mostly a way to send data in such a manner that you don't need to do the full 'call-setup-data-transmission-and-terminate' that would be required for other virtual circuit based protocols such as TCP when you don't need all that luxury. So for protocols that carry small amounts of data in a manner where retrying is not a problem and where loss of a packet is not an immediate disaster. It's also more suitable for real-time applications because of this than TCP (especially true for the first packet). Because of the fact that there is no virtual circuit a single listener can handle data from multiple senders.

It is possible that someone wants a virtual circuit but can do better than TCP for their application. I think the parent's explanation was more apt - it's a small layer on top of IP for you to implement your own protocol logic.