The things that are not files or data.
WHAT LIVES OUTSIDE THE OBVIOUS
Cron jobs Email accounts and forwarders Email filters DNS zone records Redirects configured in cPanel PHP version and INI settings SSL certificates, if manually installed FTP accounts
A full cPanel account backup includes most of these. A plugin backup includes none of them.
WHAT TO RECORD SEPARATELY
DNS records, particularly if hosted at Cloudflare or another provider, which a cPanel backup does not cover Third-party service configuration Payment gateway settings and webhook URLs API keys and where they are used
HOW
A simple document, updated when things change, stored off the server.
WHY IT MATTERS
After restoring a site you will find cron jobs missing, email accounts absent, and integrations broken, unless you know what they were.
THE TEST
Could you recreate the account's configuration from your records, if the backup restored only files and a database?