The concept of Least Privilege is applied to developers and software testers all the time to advocate that the application be developed and tested using the lowest privileged account possible to get the job done.  For our purposes (network administration), I am referring to using administrative accounts for administration only and regular user accounts for everything else including word processing, research (aka web browsing) or the ever popular solitaire!

This is about using the proper tool for the job. If you wanted to trim some leaves from a tree you would be thought a bit odd if you decided to use a chainsaw, especially if the same job could be done easily with a pair of scissors.  Why is this something almost everyone recognizes as inappropriate?  Because the potential for you to do damage is huge! There are certainly people out there who will be able to perform the task with the excessive firepower and not lose a limb, but why take the risk?  As an administrator, hitting the delete key by accident and inadvertently accepting the confirmation becomes a major problem as the odds of you having the rights to carry out the delete are much higher then if you were logged in as a normal user.  When you delete a directory on a network share you can’t just go to the recycling bin on your client machine to undo the damage.  Administrators even have the ability to change the permissions at the root of a system volume which will usually render the operating system unusable (requires a restore or rebuild).  Why would you want to have these unnecessary risks when it could cost days of downtime.  Claims that it is inconvenient to keep track of two logins are the most common justification.  Now that network operating systems have tools like the Windows “Run As” this is a hollow excuse. 
See developers and network professionals are that different after all!