is \1 vs $1 a necessary distinction?

[Dave Storrs]

Both \1 and $1 refer to what is matched by the first set of parens in a
regex.  AFAIK, the only difference between these two notation is that \1
is used within the regex itself and $1 is used outside of the regex.  Is
there any reason not to standardize these down to one notation (i.e.,
eliminate one or the other)?

                        Dave