as @jordana mentioned, this randomises your MAC. If you have DHCP reservations or e.g. various MAC rules on the router, this will bypass them. If you're installing Cockpit for the first time and through SSH, you're gonna have a bad time. My SSH session went down during install, so I couldn't see what was really going on. And that sucks, the install should have at least warned the user that such thing will happen.
And even if you apt purge Cockpit*, your MAC will still be randomised on every system reboot. It took me a while to figure out how to fix this. But even so, I rather restored a backup via Timeshift afterwards.