If you were arriving at YSBK and were going to land with reserves intact - but not a lot more (perfectly legal) - you might wish the tower to know you cannot comply with the utterly moronic 'hold outside zone' instructions that might/would follow there being already 6 aircraft airborne in the zone - not unusual on a sunny sunday. Still rather than declare a 'fuel emergency' as a first option I might wait and see what the zone loading was like first.
Yet one more indication of a lack of joined up thinking occurring at
C&%t$
Against
Sensible
Aviation re GAAP/Class D procedures.
Edited in deference to etrust