"Why play music from your hard drive? No Ads, No Privacy Terrors, No Algorithms"
- Storage cost is trivial even with multiple backups
- Can be better quality than streaming
- Available offline, forever, at no extra cost
Sure, in some jurisdictions it's not legal to rip CDs you own but it's easy enough to defend morally if you're doing it for private use.
If you're going to rip your CDs, you should consider ripping to FLAC and Opus. The only reason to rip to mp3 is that basically every legacy device out there understands the mp3 format and knows how to play it. If you're playing back on a phone or PC or a more modern device, you should use a modern format. Both FLAC and Opus are totally open source.
FLAC is lossless and will reproduce your source CD bit for bit, but in a compressed format. Listening to music in a FLAC format is the same as listening to the original CD. Opus is a lossy format, so you lose some fidelity by necessity, but if you make that trade it's the best quality you're going to get. A double blind test had it outperform AAC and Vorbis, and significantly outperform mp3.
I rip my CDs to FLAC and store those files on my NAS. Then I convert the FLAC files to medium quality Opus files and those go on the SD card in my phone. I don't use old mp3 players, so I can do without mp3s.