How can intelligent access security improve energy efficiency?

Access security systems provide a way to monitor entry and exit to a building. When coupled with a building management or energy management system substantial energy savings can be achieved using zoning to only power up and heat or cool those parts of a building or office that are to be used. This can be taken a step further using smart-phone Apps allowing a person to signal the access control of a change in their time of arrival (earlier or later) allowing the energy management system to make changes to the profile for the zone or zones that person normally works in. A good way to think of this is in terms of standby energy. Why power up a workstation of a person is not there?