Here's an example where it gets it totally and blatantly wrong:

The endpoint is a house at the right edge of the screen. The via point is the airport in the top left.
The route to the airport should have taken me straight down the interstate to the airport.
Instead, the route took me off the interstate, down Causeway, up W Esplanade, back up Clearview, and back to the interstate. That's
10 extra minutes, for no reason whatsoever.
I've highlighted the incorrect route in green, and the correct route in yellow.
I've seen some pretty bad via-point routing, but this is a particularly egregious example.
crazed_out wrote:As far as I can see Waze loves its routes. So much it will only calculate the shortest possible deviation from the original route when adding a stop. When you pick your destination a calculation happens and the resulting route is the one used for the trip. Adding a stop will not cause a recalculation for the entire trip.
When a stop is far off your route it is more efficient to set the stop as your destination and the set the new destination when you arrive at your stop.
I've seen that, to an extent, but Waze is far more forgiving when a stop point is not set. We'd be better off if the two routes should be calculated separately and then added together.