If you keep one key per device, you can revoke it if/when that device is compromised, stolen, etc..
That key is for initial access to provision your machine, after which you should have a more sophisticated means of managing users, as certainly, if you are doing anything of much importance, you will eventually need at least 2.
That key is for initial access to provision your machine, after which you should have a more sophisticated means of managing users, as certainly, if you are doing anything of much importance, you will eventually need at least 2.