it's quite complex isn't it
there's no doubt that after the event some cctv can help trace a person's movements and help the police put together parts of the jigsaw
I used to live in a street that was, er, lively. It definitely got quieter for about a month. Then people got used to the cameras, then in what I still regard as one of the funniest nights of my life a bunch of locals worked together to take two cameras down and steal them. It took hours, nobody noticed the pictures going off, no patrol car came by.
I think what I've learnt with most cameras is 'relax', the money they've spent on cameras has left less money for human resource so there will most likely be nobody watching in a little office somewhere and even if they are, the police won't have the resource to do anything about anything. But if you are stabbed, they'll have a record of it so you have a better chance of getting on Crimewatch with an appeal.
When we'd had our cameras installed I presumed the shop ram raid would be picked up instantly. Nothing happened. Eventually I phoned the police like a good citizen (I thought it might result in the alarm being switched off too). On phoning the police, I told them there was a shop raid going on right now, get here now and you'll have them cornered inside the shop. I was told the policeman that had answered the phone was on his own and couldn't come out - as he had to man the phoneline.
On another occasion I phoned the police about a burning car in the High Street - I was asked what town the High Street was in. The phoneline to the local police station had been diverted to a HQ building in another county.
I wouldn't overly worry about cctv.