Good article.

I have found that adding in the nt authority\system is a must, if you use enterprise backup software (brightstor or backupexec) as they don't log into the server as a domain account very easily.

Also Knowing the SA password is a must, when you remove the builtin\admin account.

For example. You are at your DR site and restore the master database on a machine which is not on your domain.

Suddenly you have lost your rights over the sql server aless you know the SA password or can join the server to the correct domain and log in