I'm sure it's contentious to say so but the thing is that we don't actually know. In theory it might mean that absorption will be quicker, but in the absence of actual empirical evidence, there's really no saying whether the effect would be significant or hold at all when assuming a sufficiently large dose and controlling for other factors. I can think of a member or two from here who succeeded without fasting, and that's to say nothing of accidental lethal SN poisonings, which most likely did not involve fasts.
Still, fasting being necessary is a claim that's been repeated countless times, and quite simply (and understandably) no one wants to take a risk and deviate from the standard procedure. If I use my SN I will certainly consider skipping it—I suspect that taking something very salty on an empty stomach could be exacerbating nausea. Of course, that is just a theory too.