It finds new and better routes as you drive on the fly. You can also use the map to look for other/better routes when you stop at the light.
And yes, asking PAX if they know better routes helps both of you. Communication is the key.
And if they still get pissy, give them 1 star at the end of the trip, just dont let them see it. I turn my screen off before $$ comes up and wait for them to walk away. Then i turn the screen on, wait for $$ and rate them.