I don't believe it is necessary for airplay, but probably is for Chromecast, Sonos, and many devices to establish ad-hoc connectivity for setup and operation.

I take this popup to mean that they want to fingerprint and locate my home network or backdoor it somehow. I ALWAYS deny this access unless the app specifically requires it, and that is rare.

WiFi based geolocationing should be a well known privacy threat by now. The popup should really communicate that better and provide tighter controls.