The question has been asked, Why it is recommended to open the program as ‘Run as Administrator’ when the user is already logged in to the machine under the Administrator group.
This article does a nice job of explaining UAC (User Account Control) and the purpose of Run as Administrator http://technet.microsoft.com/en-us/library/cc709691(WS.10).aspx
When logging in to Windows 7 or Vista the user’s full administrator access token is split into two access tokens: a full administrator access token and a standard user access token. During the logon process, authorization and access control components that identify an administrator are removed, resulting in a standard user access token. The standard user access token is then used to start the desktop, the Explorer.exe process. Because all applications inherit their access control data from the initial launch of the desktop, they all run as a standard user.
This is why it is important to run the program with the ‘Run as Administrator’ privileges on Windows 7 and Vista. This ensures the full administrator token is accessed and the program launched is able to access registry and other system files with the necessary full Administrator permissions.
You can find more information in Windows Start > Help and Support > search for ‘Administrator’ then topics: How do I run an application once with full administrator access token or Installing programs: frequently asked questions