Originally Posted by sweeks

The benefits may seem dubious to *you*, but many cyclists don't feel safe in traffic without a mirror. I am one of these.
It should be noted that there is very little information available about the prevalence of rear-view mirror use and its relationship to cyclist safety, so your opinion can't be definitively refuted. Neither can mine be strongly supported. The League of American Bicyclists published THIS PIECE in 2014. It has its flaws, but according to the information presented, 40% of the cyclist deaths tabulated were "struck-from-behind" interactions with cars. These are the sort of events that might be expected to be made less likely by the use of rear-view mirrors, but mirror use was not addressed. More studies are needed.