It reports core files that have been modified and files that exist in core folders but should not be there. That makes it a quick way to spot tampering with the base software.
The result is limited in scope. The command covers core only, not plugins, themes, uploads or wp-config.php, and a clean result does not prove the site is free of malware because an attacker can place files elsewhere.
Use it as one check among several. Combine it with plugin and theme verification, review of recently changed files, and log analysis. Run it again after any update or cleanup to confirm the final state.