Yeah. I have a Synology and backed up everything except... this PC. It was just the "gaming PC" and then I realized that I would rather not re-install everything and try to recover the drive. It's set up on the Synology now.
I have this with movies. I don't back them up because of the storage requirements. Everything is ripped from BluRays that I own, but... can I be bothered re-doing them?
If you'd already built out the automated "Some stranger on the Internet ripped it for me" workflow you could say that usenet is your backup.
A buddy just gifted me a decomm'd Synology RS2416+ w/ expansion unit full of drives that could, just, back up what I have... and I am definitely not going to do that.