I commute on my road bike (with Shimano 105 SPD-SL road pedals / Specialized Sport BG road shoes)
and also commute on my hybrid (with Shimano 520 SPD and Shimano MTB shoes)
no difference at traffic lights as I trackstand on both bikes
only real difference for commuting is ability to walk properly in the mountain bike SPDs if I get the rare puncture, or need to walk with my bike for any reason (like road works requiring a walk 200M down the pavement with the bike)
for riding itself? the road SPD-SL is a much more efficient platform when really putting the power down, the MTB pedal system actually feels very unstable in comparison