Google Maps automatically caches areas around your common saved locations (e.g. Home and Work). Outside that, what's the value? It's a bit niche to open your map for a cached rough outline of the planet.

I do wish the apps were a bit less stingy about letting you choose to fully offline large areas more easily though. The detailed road information is helpful when you don't have signal and if you travel for work it's often outside what a single box will capture. E.g. Google Maps lets you offline as much as you want (as far as I can practically tell) but you have to do it in many about-indiana-sized-rectangles instead of just saying "save these states" or being able to zoom out farther to a region directly.

Are you sure it doesn't? Google Maps on Android does, for me.

Zoom into some location you've never looked up before, in some country you haven't been to. Turn on airplane mode. You can pan around and the nearby areas will still be there. Zoom out, and previously cached tiles will still be available. Go to some other part of the world, and a coarse resolution version of their polygons should still be visible.

I think as of a few years ago, it also auto-caches tiles along a navigation route, but I can't find the announcement stating that anymore :(

I would think there are may reasons Google might do this; One may be if you have to download the data, they get to collect that data for use. Data for them is a commodity and being able to know who/when/where specific map data is being downloaded might be valuable. All hypothetical of course..

Apple Maps at least, seems to have coarse resolution without needing to actively browse the area first.

Apple Maps does this. I just confirmed it last week when I was international. I was honestly surprised at the detail in areas I had not marked for download.

What is the benefit of a map cached at a coarse resolution, though? does it let you navigate?