Isn't the main point of a Holtey is that they are glouriously pointless? Everything is a celebration on doing things as close to perfection as possible. If a tight mouth is neither advantageous or disadvantageous, it seems to me that fudging it at the last by making a crudely coarse mouth is incongruous unless the maker has a good reason (and the 2mm that has been reported earlier IS crude compared to the fine tolerances elsewhere).
Bugbear, I also said myself that a fine mouth makes the plane more controllable at the beginning and end of the cut. I still believe that on rather uncompliant endgrain timbers (Rosewood, Swiss pear etc.), there is a more of a chance of chattering, which I have observed is reduced with a finer mouth. And there is still the chance of using the plane on long grain. Why preclude the plane from being able to do this, for no advantage elswhere?
Of course 2 tho is probably pedantic, but 1/32 is not what I'd call fine either. !/64 is the right sort of margin and does not hamper the planes use in any circumstances that I put it to, so that setting is never changed on my shoulder plane.
Mike.