Used in conjunction with a brain sat-nav is fine. Unfortunately a lot of users disengage their brains and blindly obey the voice from the dashboard.

One problem with them is that they take no account of a vehicle's size, motorcycles or articulated lorries all get sent on the same route. I live in a rural area where we frequently have walls demolished and trucks/coaches stuck on roads which are clearly signposted as unsuitable for large vehicles (or in some cases bridleways which are unsuitable for ANY vehicle) - it's never the drivers' fault, always the sat-nav gets the blame.

I guess artificial intelligence still needs a bit of human assistance from time to time.