I started using one because I was fed up of having nothing to use to hold careless drivers to account, and if one of them did bop me off there might at least be some evidence of what happened.
About a dozen drivers have been contacted by the Police as a result of reports I have made (the majority getting "words of advice"). The incidents have been close passes, tailgating and one incident of threatening behaviour.
I nurture a (perhaps naïve) hope that some of those drivers may have decided to drive more carefully around cyclists in future.
That is the only way in which, perhaps, having the camera may have improved my & others' safety in respect of these few individuals. I prefer it to shrugging my shoulders & meekly accepting the danger, or getting into potential arguments at junctions.