Let me just explain to give you a better idea of my situation, because i personally don't think that all retail guards need a vest either.
I previously worked as a store detective at various stores and regularly came into contact with drug addicts, etc and had a few violent confrontations, luckily never had a knife pulled out on me. I was young at the time and new to the industry so wanted to prove myself and always tried my best to never let anyone get away (learned from it now though.)
For just over 2 years now, i have worked retail uniformed night shifts at various stores and it's been pretty much the same, drug addicts, drunks, groups of teenagers, had a few scuffs and other incidents taking place that didn't directly involve me (staff member getting attacked, gangs of teenagers kicking off, etc) but it's not like my store detective job, if i feel like i have no back up (no managers around to assist at the time), i can just let people walk away and nobody has an issue with that. I always put myself first and other skills that i've picked up also help me avoid getting physical, i don't think i've even had to physically detain anyone in the past year.
I am now moving store to a "high risk" store which is one of the worst stores for theft and just trouble in general. I will be alone, it will be nights shifts and i have worked there in the past so i know how bad it can get. It's in a city centre and surrounded by bars and clubs so the drunks all come over after kicking out time and this is when you get the most issues. It's basically like working the door but at a retail store, so this is why i am considering getting a vest.