Power chains for braces?

I've had braces for a couple of months now, and my teeth have been moving fairly quickly. My ortho said that to put a power chain on my bottom teeth again after having taking it off a while ago he would have to put one on my top too. The thing is, my top teeth aren't completely straight yet. I'm just wondering, will the chain on top help straighten my teeth, or just close gaps (even though there aren't any on top)?