So what would be the purpose of putting "VFR GPS" in the remarks section for
such flights?

I usually start out filing mostly direct (other than through the passes
and mountains). ATC always says no and gives a bunch of airways
depending on where all the jet arrivals are. Having "VFR GPS" seems to
help in that the controllers will often offer me ad-hoc "short cuts" in
the airway routing when there are holes in the arrivals.

-Robert