Hiring a security guard has numerous benefits. At the most basic level, the presence of a manning guard can be enough to deter a thief. This is because a stationed officer communicates to thieves that their chosen target will not be an easy one.
As well, a security guard can be trained to detect potentially threatening behavior, meaning a higher chance of that behavior being curbed before it even becomes a problem.
Another benefit is that a security guard can react right away if there is trouble afoot. Unlike a security camera, which simply records security breaches, a guard can address problems immediately.
Even having access to a security guard company's phone number can be enough to defuse situations when they arise during working hours. There is little more effective than saying "I'm going to call security" when a situation looks like it's going to get out of control.