A mystery

You answered your own question.

A "little time difference either way".

If you have your Garmin set to "fastest" routing it is likely that your unit is factoring in right turns to maximize the possibility that you can utilize any "right on red" situations along the route.

My Garmin Nuvi is doing the same thing as yours. For me is all street level roads one way and a mixture of streets and highways on the way back. I have mine set to "fastest." I have not yet tested the other settings and avoidance configurations to see how it changes the routing.

Where I am, the on/off ramps on the highways I'd be using simply are a little funky going in one direction and are much more straightforward going the other way.

If you interpret what he wrote as "the same" or "almost no difference" than it isn't obvious why Garmin would choose one way over another for the same A to B and B to A trips in opposite directions.

I know a lot of times I "stop" routing close to my destination. If I were to drop off something, the GPS might have been off when I took the key out of my car (cig lighter not hot when car is off).

Then if I select "Go Home" when I return, I might be in a slightly different location.

What was your situation?

What the GPS thinks about turns on a route is not always what the user knows about the upcoming turns. That is why some of us report to NavTeq problems we encounted when routing is obviously out of kilter with reality.

Thanks for the replies. I did turn off the ignition at destination but set the GPS up for the return journey before setting off. Interesting that it may be avoiding left turns which, I believe, is a feature of the overnight delivery service (UPS etc) routings.

Will see what happens on future trips; will try not turning the ignition off next time.

Depending on distance between points, there might be many factors that come into play. Divided or limited access highways that have different points (intersections) for on- and off-ramps, different speed limits, school zones, or one-way traffic patterns, etc. Even a difference in the way a thoroughfare enroute is named in the GPS's data (Hwy 1111 vs. XYZ Freeway) may impact the routing.

I noticed the same, instead of taking Hwy and left turn, it routes me a little past and right turn on Hwy

The garmin has a setting that allows you to chose between least time and least mileage. Try changing your setting to see if it routes you differently.