This is just my view and only from my own experiences in the market place I work. I'm sure there are many more valid opinions.
I've been in the electronic security industry for over 35 years now and in my experience CCTV is no deterrent. CCTV, if recorded, will give you a nice visual record of some scumbag damaging your property and nicking your valuables. You will be able to watch it over and over again while the Police will do absolutely nothing with the footage because they 'cannot' identify the suspects. For identification you'd need at least 250pixels/m at target distance and you'd still struggle as invariably they would be wearing hats, balaclava's and the like. For most normal domestic premises CCTV can even have the effect of advertising that there may be something worth nicking.
When CCTV starts to work is when it is monitored and using a decent form of detection. By alerting you or an operator in a monitoring station any threat can be visually assessed and action can be taken that prevents damage and loss. Switching on lights and using audio to tell the intruders that they are being recorded and the Police have been called is usually enough to have them on their toes.
The biggest deterrent to would be intruders is light and dogs. Powerful lights coming on and dogs barking are far more effective than standalone CCTV or indeed intruder alarms.
I have access to some of the most sophisticated electronic security that there is and for my domestic security I have a simple intruder alarm and make sure I lock the doors and windows.
Neil