What about the scenario where there was a conflicting aircraft on descent into Coffs? As others have said, you've got to be ready for the worst.
Inbound IFR aircraft do not just 'pop up.' That's not how an ATC system works. They are known about well in advance through co-ordination from the previous controller. The Tower also gets a departure message from the AFTN network.
There is a culture of 'clearance not available' to VFR aircraft in Australian ATC. It's ingrained from day one of ATC training.