A quick way to convert a negative to a positive in PS is to click on "Image", "Adjustments" and "Invert".
That's true, but doing it with a Curves Adjustment Layer then also allows you to make further luminance adjustments in the same tool and its completely "undoable". Using the method you describe of course works and would also be "undoable" if performed on a duplicate image layer, but then an Adjustment Layer would be required on top of that for further Luminance editing. And we are talking B&W. It gets more complicated when dealing with colour negs.