Applying the Principle of Least Privilege to User Accounts on Windows XP
April 11, 2006...
The Least-Privileged User Account Approach
A defense-in-depth strategy, with overlapping layers of security, is the best way to counter these threats, and the least-privileged user account (LUA) approach is an important part of that defensive strategy. The LUA approach ensures that users follow the principle of least privilege and always log on with limited user accounts. This strategy also aims to limit the use of administrative credentials to administrators, and then only for administrative tasks.
...
Source: http://www.microsoft.com/