It's a treasure. I understand why most people don't do this, but I will probably forever.
A really significant amount of it isn't otherwise available on streaming services. While I'm an Apple Music subscriber, I still acquire my own mp3s for most of the new music I listen to.
iCloud Music Library is an immense value here as well. Rarely it will sync the wrong version of something in my library, but usually it's on the money. The fact that it doesn't cost anything extra on top of an Apple Music subscription is a huge boon, and it doesn't count against my iCloud data either.