The rh outside rear view mirrors where kind fo like the rear-mounted radio antennas were in the later 1950s to earlier 1960s.
The lh front mirrors were optional (before they became standard equipment), so if ONE was good on the lh side, one to match it on the rh side evened things out for a more upscale and balanced look. On the back with the antennas, usually one was a dummy, for looks rather than better reception, although some did hook them up to work together (via a kit from JCWhitney).
Putting the mirrors on the fenders was supposed to mean "just a quick glance" to see rearward, rather than turning one's head, but with their smaller diameter, not much of a field of vision as the inside mirror provided. Worse on the rh side. Larger diameter mirrors would have not looked good. About the only thing the rh mirror provided was the rh frt passenger's capability to see rearward.
So, other than for ornamental purposes, not nearly as advantageous as many suspected they would be, except in very tight parking situations, as
@Big_John mentioned. In general, the cars were designed to have great driver visibility rearward.
Just some thoughts and observations,
CBODY67