I tend not to use my camera now as most of the time I am doing my best to avoid busy roads as I no longer commute, however I wore it virtually all the time when I was.
I got one after I was threatened by 3 blokes in a truck, they had obviously all been drinking, they pulled alongside me so the passenger could have a go at me and when I turned off they back-tracked to come back at me a second time, I reported the incident to the Police but video evidence would have gone a long way to finding them and possibly prosecuting (I wouldn't have held my breath!). Two days later I was very nearly taken out by a van overtaking a car coming towards me, the driver clearly saw me but decided to overtake anyway (the laugh and wave as he passed was the give away). I had been thinking about getting one prior to this anyway, as the incidents of close passing on my 29 mile round trip, commute over mainly country roads, seemed to be on the increase.
I realised that the chances were that if I had been killed or seriously injured in either of those incidents the perpetrators would almost definitely got away with it and my family would have forever wondered what had happened. I felt, and still do, that I won't get justice, but my family might get some answers/closure.
I suspect most of those who use cameras do so because they have been subjected to incidents like mine.