I have wondered about the difference of using right vs left for right turns. Using the arm on the "road side" may be more visible to vehicles, although pointing where one is wishing to turn is very clear to everyone.
I'd use both arms, but I don't like riding without hands (an experiment gone wrong many years ago).
I usually only signal right when it would "make a difference". Cars pulling out of a road I'm turning into, cars coming up from behind, and could make the turn around me, etc.
For left turns, I usually verify the path is clear before making my move, but still am more likely to use a left signal if there are cars somewhere back there.