A surveillance system today can easily have hundreds of cameras. It would take several operators to view this many cameras even with a sequencing system switching four monitors per operator every ten seconds. This arrangement still leaves too much time between images for adequate surveillance, not to mention the fatigue factor it induces in human operators.
The answer is either more staff to monitor the video, which could become cost prohibitive, or a system that is intelligent enough to analyze incoming video, detect a problem and signal for a response or initiate a predetermined one.