Just mulling over this, checked Jepps and I see under Departure, Approach and Landing Procedures:
....with the exception of Australian and New Zealand operators and aircraft conduction independent visual approaches at Sydney, Super or Heavy jet aircraft will only be assigned a visual approach when:
a. specifically requested by the pilot, and the pilot has reported the landing runway in sight; or
b. the straight-in approach aid is unservicable
Still curious as to why it's necessary to issue a visual approach clearance?
UTR