Protection of client from an armed adversary.
Armed guards must be trained for the circumstances of firearms and must avail a license to carry weapon. This is excluded from the part of training and experience which you need to become an unarmed guard.
Perhaps, armed guards play a vital and difficult role to achieve the training and they also have to carry a calm temperament with a complete understanding of the conditions that prevail in the environment they will be working in.
Usually armed security guards are only employed in a situation where items of substantial value need to be protected. This includes antiques, cash, works-of-art, jewelry, rare books, valuable documents or important people.
They do a lot more than just guards. Escorting funds to banks and other financial institutions, escorting valuables or cash from one place to another within a facility and they physically make sure that protective systems such as alarm systems and safes are active.
Armed guards are generally never employed in a marketplace on an ordinary day because experience has shown that unarmed guards are sufficient to demolish crime in large department stores malls and sports venues. But things could be framed according to circumstances and an armed officer can be called anywhere if the situation requires protection of client from an armed adversary