Do you want to stream music from an app on your Mac to your HomePod? Good luck with that. The only app that supports AirPlay streaming is iTunes, and what’s the point in using that if you can stream your iCloud Music Library directly using the HomePod alone? For apps like Spotify, or VLC, you can resort to streaming your entire Mac system audio via Airplay, but then you have to listen alerts booming through the HomePod, and you can’t remote-control the Spotify Audio using Siri.
But if you use Rogue Amoeba’s AirFoil, you can fix all these problems.