...which speed
Vref,
Historically, all-weather approaches would involve some manoeuvre, lateral and/or vertical. Nowadays this is more relevant to a NPA or some Cat 1 ILS approaches, but with RNAV FMS etc this is less of a problem.
The higher category margins provide additional time to manoeuvre at higher speeds and to a lesser degree consider the aircraft inertia and ability to manoeuvre; again these are now less of a problem.
However these category additions also apply to holding patterns, joining, and intermediate approach procedures; and perhaps of greater relevance today, for missed approaches.
Thus it could be hazardous to assume that the use of a single category will cover all circumstances.