Aye, sorry for the OT conversations!
I guess they are ultimately there for realism - they're on the real organ, and the Hauptwerk sample set aims to mirror that organ as fully as possible.
I for one have great pleasure demonstrating how great Hauptwerk and its wind model are by turning off the blower on my Skinner sample set whilst playing. I gess the Afsluiting won't have the same effect, probably more instantaneous, and actually, I'm surprised I haven't tried them yet!