After a recent good run, it seems the MEL-PER route has returned to its old habits with the JQ972 8.00am flight across to the west (and the return journey JQ977) having been cancelled at least the past four days. All well and good if you're on a sector where there's a flight every hour or so and you are easily accommodated (however inconveniently) later on that day. However, there are two JQ flights per day at most on this route, with a wait of 15 hours until the next one - departing 10.50pm and arriving the wee hours after midnight into Perth. Not the ideal situation if you've planned an interstate weekend away.
As discussed quite frequently before (with Melburnian1 trying to get to the crux of this matter) - (a) how much notice do the PAX get of any change in schedule? (they are selling seats on these flights seemingly up until the day before) and (b) are you simply scheduled on this later JQ flight or scattered amongst the QF flights throughout the day? One can't imagine only two half-filled JQ flights being combined, so there must be a QF involvement here. Are these then prioritized according to QF status or JQ Max/Bundle ticket holders ? One may play the devil's advocate and say if they were guaranteed a QF flight and were given sufficient notice, you'd purposely buy a JQ ticket at a cheaper price and sit back, waiting for your "last minute cancellation" and told to hightail it over to T1 instead of T4 and head on up to the Qantas Lounge.
I know Melburnian1 has suggested in the past that, in fact, it may be the Qantas loads which are down on the day and, rather than disrupt those business & higher-fare paying passengers, it is a better business decision to change the plans of the mere Jetstar flyer. It would definitely be good to hear of any first-hand experience with this - I know nobody here seems to admit to being a Jetstar patron, but perhaps one or two are willing to come out from the shadows and give us some details.
