Pervasive security cameras don't substantially reduce crime. This fact has been demonstrated repeatedly: in San Francisco, California, public housing; in a New York apartment complex; in Philadelphia, Pennsylvania; in Washington; in study after study in both the U.S. and the U.K. Nor are they instrumental in solving many crimes after the fact.
They CAN be useful, in limited circumstances.
...Used properly, they're effective in reducing crime in enclosed areas with minimal foot traffic. Combined with adequate lighting, they substantially reduce both personal attacks and auto-related crime in multistory parking garages. And sometimes it is cost-effective for a store to install cameras to catch shoplifters or a casino to install cameras to detect cheaters.
But these are instances where there is a specific risk at a specific location.Schneier's conclusion? Dump (most of) the cameras.
Hire cops and train them well.