I'm not sure I've seen anyone drive further than about 10 minutes away without Google Maps in the last 5 years.

Or maybe everyone's misunderstanding your question?

I don't really understand why anyone would need sat nav for a ten minute drive.

Neither, but my coworkers are apparently unable to carpool to a lunch spot 5 mins away that we visit every 2-3 weeks without setting nav first.

Once the city you live in gets large enough, memorizing the routes just becomes a non starter. I have my route to work almost memorized but due to construction or crashes it changes so often it is hard to cement it. (Seoul)

Because the traffic isn't known to you but it is to Google. I could take two routes, one is faster depending on circumstances, and Google knows those circumstances.

Is it really faster though?

All you have now is two routes with a roughly equal amount of traffic on.

One of those routes will be a massive detour.

How do you know those routes have a roughly equal amounts of traffic? Or that there’s only two routes? I usually see at least three possible routes with my commute (with some forking), and at least one shortcut. During heavy traffic one optimized route can at least save 10-15 minutes than the slower one(s).

It's really unlikely that you're saving any time at all.

And you know this how

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