[TurboFool]

As far as the final result, there's no advantage. You get the same ROM on the same phone either way. The advantage flashing from the card serves is no ActiveSync connection issues, no requirement to use a compatible OS, and the ability to easily flash when not in front of your computer. I also find it flashes faster. To me it's a big deal to have several stable ROMs sitting on my card so if I suddenly have a major problem (like 5069j's time bomb), I can easily plug the card into any computer, move the nbh file I want into the root, and flash it. But in general it allows me to just throw a new ROM on my card before I leave for work or something and then flash when I have time. Very convenient.