Technology is continuously improving the nature of security systems, and making it harder to enter an unauthorized area, or at least very difficult to do so without being identified. There are even some security operations that rely entirely on machines with no human involvement. This can be an ideal solution for some properties, but in many cases securing the post will demand skills that a machine can never possess.
The primary goal of all security systems is to deter an intrusion before it happens. While all visible security measures have a deterrence factor, no fully automated system can be as effective as an active authority figure on site, capable of making what they judge to be the best possible reaction to any incident with no delay while the automated systems contact police or the property owner. Security personnel are often required to interact with workers and visitors, which has many benefits including fostering the feeling of being protected.
Many times a security officer will need to mediate on events, or make other judgment calls, for example determining that someone is too intoxicated to be allowed to enter an event. The value perhaps proves itself most when an incident does occur, and the security officer immediately becomes the first eyewitness. A human can always put more detail and more relevant facts in their reports, and cover the gaps such as sound or the area outside a camera’s field of view. A video recording of an incident backed with a report offers an unparalleled illustration on what the facts of the situation were. If only one of those assets is available, determining the full details of the incident can be much more difficult, if not impossible.