As a former security officer with several years experience, I can say:
The weapon is used for the same reason as we all use it, self defense. It can also be used like LEOs use it in the course of apprehension or to protect clients. This of course varies state to state and is dependent on what the employer allows. My assignments were mostly high crime areas: low income food store shoplifting details, construction, section 8 housing community patrol, late night fast food joints, etc.
I never stood at the front door while in uniform, despite the managers' demands. Once I explained why, they mostly understood.
Plainclothes is an option but does not act as a deterrent. Was working a grocery store once that was robbed while I was there. Had just come around the front, walked to the back, when they called for help over the intercom. I'm sure I was made,anyway, since I was the only white guy in the ghetto.
Uniformed or not, I preferred irregular passes around the front or retail locations, loitering in the back at odd stops. NEVER set a pattern.
I never worked unarmed. Sometimes I had 2 backups as well as an economy size pepper gas and baton, long arm in the vehicle. When you're in a deserted location, you want all the luck you can carry.
One December I was posted in a liquor store all month. Lost count of the number of sober patrons that thought I was a cardboard cutout until they tried to get around me.
Most people don't see that you are armed or unarmed. They see a uniform. They recognize that you are not an LEO, other than that they don't care. The area I worked in, and I suspect that this is true more often than not, was not usually what you'd think of, as a "normal" citizen of the community. I dealt with a subset of society made up of criminals, thugs, partiers, juvenile delinquents, white trash, homeless, and the occasional "shouldn't be out at night" citizen. And of course the employees of certain establishments, that may or may not fit into one of the mentioned categories.
My "clientele" knew I was security, but also knew I wouldn't hesitate to arrest them or get into a scrap. We knew each other in an institutional sort of way. The ground rules were pretty established. It wasn't like your typical soccor mom running into me at the mall and wondering exactly what I could or couldn't do. They respected my authority, and occasionally challenged it. It was rare for me to work with "normal" people, although I did work a couple of malls, armed. Used to get people in the malls asking/telling me that my gun wasn't loaded. Haha!
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