Yup, this is extra useful when I'm using e.g. an external USB headset for calls. I can have media played through my speakers while using the headset for calls,

Yup, this is extra useful when I'm using e.g. an external USB headset for calls. I can have media played through my speakers while using the headset for calls, regardless of whether or not the application supports this itself. (Admittedly VoIP applications generally do.)