This is not only about space (as you can fit 32gb sdcard in your phone to preserve more cached data) but also about battery life.
My short test at earlier project stage shown huge impact when maps are generated in realtime with vector area or even vector vs raster tiles. Also, maps are highly detalized (as almost all data from osm xml is used), and requires POI icons, so svg tile was bigger than png with custom palete.
I'll test things again show some numbers.