I can't think of a reason why trailing vs. leading per se should matter, but inner vs. outer matters in the amount of bend it puts at the flange head. Hold an inner and out spoke side by side and the effect is easy to see. But it's easy to keep them straight just by putting them in separate piles as you disassemble the wheel, so you don't have to examine them to see which is which. And for the rear wheel left vs. right might matter if they are different lengths.

FWIW, I agree that taking the wheel apart should be done slowly. De-tension the spokes a little at a time to avoid pulling the rim out of true.