[MetroMPG]

Reversing in has the added advantage of being generally safer, too. And the reason (better visibility when leaving the spot) is yet another contributor to better efficiency: if you can see, you can wait to start up and just go when it's clear, rather than creeping slowly out in reverse until you have a good view & an opening. (Assuming vehicles on either side creating visibility issues.)

Of course it's one of those miniscule differences. But the pennies do stack up.