When it saves money
When the National Whimit Pass is worth it.
The National Whimit makes sense if you are doing a true cross-country itinerary, combining the East Coast (Melbourne→Sydney→Brisbane→Cairns) with either the Stuart Highway corridor (Adelaide→Alice Springs→Darwin) or the Top End/Kimberley spur (Darwin→Katherine→Kununurra→Broome), with at least 4–5 long-haul legs in the window. The 30-day at $575 is the sweet spot for most travellers covering more than just the east coast. Note that Cairns and Darwin are not connected by a direct Greyhound service; getting between them requires backtracking via Townsville, Mt Isa and Tennant Creek with overnight transfers.