When is it necessary? when entering an important command into a critical system that affects thousands of users.
Or when you have to review your network to make sure no holes are found.
the attacks on your network are relentless:
Bad hackers 
will attack your network and own your machines.
Once they own your machines they will use your machines to attack others. It is important to double check your machines for any holes, it is what prudent businesses do.
[…] You must do something about this threat http://oversitesentry.com/spoe-second-pair-of-eyes/ What you should be doing is testing your systems, making sure that your computers are not vulnerable […]