None. I think one needs a very good pressing reason to build spoked wheels with less than 32 spokes. Even with 32 spoked wheels I tend to suggest getting a slightly more robust rim than I would advice for a 36-hole build. This is especially true with road wheels due to the dish. Its not that one can't build a useable set of wheels with 28 spokes and a heavy enough rim but the stresses from some peak loads and the failure modes makes them anything but "reliable". On the track wheels sometime, as in Indian films, cross and, on the road, braking using rim calipers, rough roads, cobblestones, pot-holes, curbs and all kinds of other "hazards" can provide loads that lead to catastrophic failure (e.g. lateral wheel collapse).
I've got my pressing reasons, thanks, and a whole heap of experiences with a veritable plethora of build specs in a wide array of riding conditions, so kindly keep the endlessly reiterated conservatism to yourself.
I've got my pressing reasons, thanks, and a whole heap of experiences with a veritable plethora of build specs in a wide array of riding conditions, so kindly keep the endlessly reiterated conservatism to yourself.