What function or code or programming utility should everyone know about and have access to?

yt-dlp

https://github.com/yt-dlp/yt-dlp

Download anything and everything on YouTube for keeps. At the best quality or whatever available quality you want. Playlist = albums/CDs/box sets, Channels > Releases/Playlists = discography

I would never go back to Spotify or AppleMusic or any other sub service