EI-MICK,
One aspect of this that I am aware of is that maneouvering aircraft are not allowed as close to the runway, so for example aircraft waiting to line-up/cross the runway in use must wait at a holding point more distant than the usual holding point.
(You usually see these holding points specifically marked, for example F3 CAT II/III if F3 was the holding point.)
The reason: aircraft on CAT II & CAT III approaches are using the ILS to a lower height, and a big lump of metal near a transmitter will interfere with radio signals - so keep the aircraft further from the runway so it can't interfere with the ILS.
Just out of interest, aircraft on CAT II appraoches have a minimum decision height of 100ft, CAT IIIA approaches 50ft, and CATIIIB approaches 0ft.
Hope this helps,
POL