The trouble with both maps and satnav comes when the road is blocked by roadworks/accident etc.
There you are, driving along at route you know well (but anything off that road is unknown territory), or have studied on the map before you set out. Suddenly a diversion sign. If you follow the arrows you spend 30mins going round in a big loop to end up almost where you started, but the other side of the block. Too dark in the car to read the map, and even if you can you don't know how much of the road is blocked.
Satnav not only doesn't know how far the road is blocked, it doesn't know it is blocked.
Now if it could have warned you in time, there would probably been a better route.