When it saves money
When the Integrity Coachlines Hop On Hop Off Pass is worth it.
It suits anyone doing the Perth to Broome run with stops (Coral Coast towns, Ningaloo, the Pilbara) rather than a single point-to-point ticket. The 3000 km tier at $399 roughly covers a Perth to Broome one-way with kilometres to spare for side trips; the 6000 km tier at $724 is built for the return.