The deterrent effect is less because clerks are more effective than cameras at detecting crime, and more because people don't like committing crimes when there

The deterrent effect is less because clerks are more effective than cameras at detecting crime, and more because people don't like committing crimes when there are other people nearby. Obviously that's not an absolute statement, especially considering that armed robbery is a thing. But in general humans are better crime deterrents than security cameras or robots. In a lot of cases, that's the sole reason for employing security guards, since the only thing they're actually allowed to do when they encounter crimes in progress is ring the police.