It's useful for gauging the skill of your opposition but it isn't always accurate. But I suppose it's a clever idea from developers to keep people playing, and stop them noticing that what they're doing is playing a single game ad infinitum, in a long monotonous drone. Possibly adding the occasional extra reward, such as extra weapons. Personally, I prefer multiplayer when you're fighting the person next to you not some faceless, universal computer generation that supposedly has a player behind it.
In essence you're fighting a hyper advanced computer, with creativity. But my competitive streak keeps me going.
But to answer the question after prevaricating for about 8 lines, I think they're a clever idea, but I don't like them. But my competitive nature with my friends keeps me wanting to get them.