The deal is, some passengers are convinced they know the best route from point A to point B, and will accuse drivers of trying to con them if they don't take that route. So if the passenger has a route they want to take, even if the route is stupid, you just shut up and do that. Otherwise, you take the best route.
In theory, of course. I have no doubt that there exist cab drivers and Uber drivers who run up the meter. Hopefully, Uber does some monitoring of routes and catches at least egregious cases.