Hm, imo it should stay. I also think people aren’t using it b/c they don’t know the difference between input and output sliders.
Let’s say you add a lot of contrast to some area you isolated in the input and in some parts you get pure black and pure white. You might wanna soften it up a bit by excluding or gradating the effect on the L extremes in the output mask.
It seems to me that output was made for a purpose and it’s better to have it and not need it then needing it but not having it.