I spent $4,000 putting in a video surveillance system at my home. I has a 650 GB hard drive that allows me to save information for weeks and easily copy videos off to a CD or USB drive. One camera looks all the way down my long driveway clear to the street, the other looks into my backyard. I agree, seeing them coming, or at least being able to gather evidence on the back end, gives one a lot of peace of mind.
Let's compare that home installation to security camera use in the workplace, using an example from a business setting that demonstrates how cameras and humans must work together in access control and surveillance:
I remember a contract armed security job I did at a major financial brokerage concern in Colorado Springs. A fired employee had called to threaten to kill people at the facility, so the firm hired us to supplement the unarmed guard force.
We did a survey of the camera setup outside, and found it lacking in some respects, such as no cameras in the parking lot in front of the building, where someone would have to park to come in. So we knew our major chokepoint for entry was the front lobby, where the workers came in droves and badged in at the desk where a single unarmed security guard was stationed.
We were also concerned by a back way in, controlled by access badges. We were concerned this person would piggyback in with someone else, or use someone else's card to get in. We had some cameras here, but they were not pointed in the right direction to closely pick up activity at the door.
Due to his mental state, this guy's wife took his car keys away from him. He came to the site several times by bus, we learned by following him. We were thankful a camera overlooked the bus stop, so the officer manning the control room could monitor at dropoff times on the bus schedule.
Technology has holes and gaps, and it takes human intellect and reasoning to come up with plans to use the technology to accomplish the mission. Same applies to the home security system. Give it some thought before you purchase and install.