I fail to understand how you can actually have a `DH of 0 ft`, [...] You would be on the runway (hopefully!) at this point anyway. What now forms the basis of your `decision`. [...]?
I think it's a legal/mental exercise. Completely unnecessary but some operations were not allowed to use CATIIIB with NO DH. Certifying the aircraft for DH = 0 underscored the stupidity of such administrative restriction.
Thing of the past hopefully now, IIRC Belgium used to be similar.