First the Pro, or in favor of/in support of:

The principal point favoring the use of having a security guard is protecting your most valuable assets.

The secondary positive point is the customers of the business or residential building feel safe.

The 3rd supporting point is going to be the patrons around the protected premises are also protected.

A fourth big benefit is the professionalism and service the security guard can give to people passing by.

And last (although not necessarily least) we have the fifth point in support the piece of mind knowing that your valuables are kept safe and secure.

And on the other hand, to help keep this balanced, there is Con; Against:

Firstly, the point against is going to be no protection against vandalism.

The second point in contra is going to be the potential loss or theft of anything on site

A 3rd significant point against is no quality control during off work hours.

4th point in contra will be the lack of first hand feedback if any problems occur.

Fifth and then finally, last point in contra is going to be personal harm to anyone onsite cannot be avoided if no security guard is on site.

Now both sides have been heard from and the Pros and Cons are stacked up, in favor and against.

So, in the final analysis is having a security guard the good thing? or just a bad thing?

We now have a "Yes" answer to both questions! having a security guard is apparently both good AND bad! It will have to be left up to you , the reader to decide. Which side, the good or the bad, has got the preponderance of weight of opinion?