For the bike like the blue one in the photo, I don't see much advantage when everything is considered. Maybe someone else will have some thoughts on that. Small wheels are used for folding bikes a lot of course, which need easy portability, so there's an exception. As for the bike peripatetic's interested in, since it appears to be a sort of touring bike, and since smaller wheels are inherently stronger, the smaller wheels would be an advantage in that regard. Another advantage would be a very low center of gravity. I've seen a 20" wheeled backcountry tourer fully outfitted with racks (I mentioned it earlier in the thread), and it's obvious the bike would be extremely stable fully loaded-