I use navigation services quite often (as much for traffic mitigation and ETA as for directions), but I never use voice guidance, even on long, unfamiliar trips. I think that offers the best of both worlds: you're never going to get seriously lost, but you still need to check your surroundings against the map frequently, which builds a mental map.

This may not be reliable if you're bad at multitasking or aren't very visual, though.