A smaller drivetrain is obviously lighter, and possibly stiffer and more responsive(better for sprinters), at least that was the idea behind the dura-ace 10 drivetrain. Basically everything's just smaller. Was on my first trackbike, works really well, still have the bike but don't ride it anymore because the parts are too hard to find.
These days though I run a 46x18 on nyc streets, and a 48x14 on the track. I think a big reason to go with a medium-ish gearing is that you generally end up with medium-ish chainrings, which are pricey to replace.