You can easily get an estimate of the number of buildings and especially vehicles, which tell you two important things. Not to mention that as a matter of course the first thing to do is photograph everything that looks like a piece of military equipment, which has been a purpose of satellite photography from the beginning.
Various kinds of countries get paranoid about letting people have maps or accurate geographic data. This makes very little difference militarily but causes real inconvenience for the locals.
Besides, nobody wages wars for labour exploitation any more. It's all about what's under the ground.
That said, my actual experience of processing earth observation satellite images was with scientific data, not spy sats, and in any case it was just over 20 years ago and may be out of date.
What I was working with, any given satellite image capture was a line rather than a rectangle, basically a rolling shutter effect but on a planetary scale and taking ~90 minutes: https://en.wikipedia.org/wiki/Push_broom_scanner