In a commercial environment, your goals are to allow “easy access” to your employees and authorized vendors or visitors that are documented.  In the case of an “event”, you can review who went in and with the use of a recorded CCTV you can tag the entry event with a video clip.  With the Web, you can look live at who’s in the facility.  With monitoring devices, these systems can signal you of a door or gate open that “breaches” your security perimeter.