Depends on the airplane
Agreed. Not just the airplane, but the mode(s) too - the FD doesn't have to be coupled to a GPS or FMS to provide proper guidance. NAV and VS does a similar job to NAV and VNAV; one is just a lot more precise for the specific approach.
Its a similar situation with setting of the rad alt. Some companies say set it always to the DH/MDH while others say only for CAT II/CAT III.
It always depends on the gospel being read at the time - AFM/(F)COM/SOP, etc.