Originally Posted by carleton

Well, it's not just a matter of fitness. Gear ratios play into how quickly you start and stop the bike. For example, if you are downtown and and going from intersection to intersection, stoplight to stoplight, then a bigger gear (even though you can handle it) may be cumbersome. The opposite is true on long flats where you can cruise at a nice constant speed.

Most of my street fixed gear riding has been in downtown in cities like Baltimore, SF, Atlanta, DC, etc... where there was lots of stop and go.