I generally use Poweramp to play music (on "album shuffle") in my car as I drive, with Waze running. Poweramp plays through my car's bluetooth audio system, and I set Waze to use the phone's speaker for its audio prompts.
When I set Poweramp to "respect audio focus", every time Waze has something to say, Poweramp stops playing entirely; stopping and restarting the audio both seem to be slightly slow. This mode of operation can be extremely annoying, particularly when Waze gives a bunch of audio prompts in rapid succession. ("In 400 meters, at the roundabout, take the second exit. In 200 m