I meant that I don't see any real advantages or disadvantages when you compare singlespeed to fixed.
Anyone who's been riding fixed for a little while can spin their legs fast enough on a downhill to be as fast or maybe a little faster than someone coasting down the same hill. It really doesn't take much effort either. Having ridden both fixed and singlespeed on a variety of terrain I can say that to some extent fixed is a bit more fun and you can enjoy that locked in feeling but other than that you can do most anything you can do on a fixed gear on a singlespeed and the other way around.
Maybe If you lived in an area with big winding hills you might want to be able to coast to lean more in the turns but then you're probably gonna want something with some gears anyway.