[minot]

> I think it’s more that it’s a fairly useless correction which makes no real difference.

You can't assume all roads are two-way/full duplex. It is possible (not sure how frequent) that going from A to B takes considerably longer than going from B to A.

[h0l0cube]

Something that's often not taken into account on Google Maps, but important particularly for cyclists and heavy vehicles, is incline, which can be very different depending on which way you're going.