I've found that downloading the 2gb of maps makes a negligible difference in the load time of each map. It took 3 seconds before and 2 seconds after.
The download stops if you put the app in the background or turn off the screen.
Also the maps are downloaded to cache... cache that can be inadvertently deleted by other android funtions... easily.
So now I don't have my downloaded maps anymore, but it's no big deal because having them didn't seem to mean much.
So for any devs reading, what I'd like to have happen is instead of downloading using your proprietary client as a host for the incoming data, instead use android to handle the data in the background so downloading it isn't such a pain in the arse. Don't put the files in cache (if possible), and DO provide documentation about what the benefits of caching all these maps are in the first place, because I have no idea what it is supposed to improve.
My guess would be that, as long as you have a decent connection (and most people probably play on wifi most of the time) the download time of one single map is negligible when you still need to connect to fetch the individual current status of the map you are loading (mobs, players, percs, resources) so while you are saving bandwidth by not downloading the same maps over and over (which would be noticeable on slow or mobile connections) you aren't actually saving all that much time.
Thank you for the feedback, it has been shared with the team.