Some administrative privileges (e.g. taking ownership of or restoring arbitrary files) are so powerful that if used with malicious intent they could allow the entire system to be compromised. With user account control (on by default since Windows Vista) Windows will strip the user token of these privileges at login. Thus, if a user logs in with an account with broad system privileges, he/she will still not be "running" with these system privileges. Whenever the user wants to perform administrative actions requiring any of the system privileges he/she will have to do this from an "elevated" process. When launching an "elevated" process, the user is made aware that his/her administrative privileges are being asserted through a prompt requiring his/her consent. Not holding privileges until actually required is in keeping with the Principle of least privilege.