And you also thought that a user cannot access cpanel when cf is activated ?
That's because THEY CAN'T!!!! How can a user access your cPanel if your server is down? CF has absolutely nothing to do with that. If your server is down, you won't be able to access cPanel.
And you also thought that all they do was cache static content ?
That's exactly what they do. Again seeing above, if your server is down, it can't serve dynamic content. CF can't run your PHP files, access your database, etc. if your server is down.
It's a pretty simple concept.