It depends on your preferences, but myself I just like knowing what I listen to a lot and send my monthly cover art collage to brag about my blorbos

The player / radio are nice, but I personally created my own radio generator based on my data

It's a scrobbling service. You send your listening data to it so that you can see your listening habits and share them with other people (your top songs, which countries the artists you listen to are from, etc.). It's just interesting data that some people like to collect, but if you only throw on your mp3s and don't care about that, then you probably won't find much use in setting it up.

Edit: to clarify what "listening data" means here, it just means the metadata of the music you play. Song name, artist, album. Nothing fancy. I think it also supports marking songs as favorites.

I’ve been living off a folder of mp3s for 30 years.

Same here. I love that shit. My mood is the algorithm. I still occasionally get new stuff, but from other sources I happen to see or hear, like a Netflix show that has it in the background or a musician's personal recommendation in an interview, and I go look it up manually. But even if I never got anything new, I already have more music than I could easily listen to in a lifetime that I already know I liked at least once.

I've tried streaming sources, but it never hits right. This way, where I am specifically picking the artist or album, it's always right, always fresh, and I'm always listening to something I want to hear.