It loads a map or GPS app alright, you will see the dot (your car) moving on the map alright as you drive, but the map will NOT ORIENT in the direction you go. So, for example, if you drive in the SOUTH direction of a north/south street, you would EXPECT the map to be FLIPPED up side down so you can see the DIRECTION you're going. Without a compass, it can not FLIP and orient the map. The map stays in a FIXED orientation. Yes, very annoying.
Without a compass, you also cannot use astronomy apps like Sky Map or any star gazing, planetarium apps. No orienteering apps (don't get lost in the woods...). I also heard that some features of Pokémon Go cannot be used properly, but I don't play Pokémon Go, so Pokémon players can say more about that.