Speedbird,
38 hour slip in LAX for BNE crew have always been there since the basing opened, (actual slip 39:20)
For the majority of crew these are the preferred trip as it is good duty hours (30:20), it's only 4 days away from your loved ones and therefore allows people to lead a reasonable life at home.
You only need to do 6 and a half of these per roster, if you are lucky enough or senior enough to get them. The beauty is you end up with nearly 30 days off per roster.
There has been a lot of crew affected by reduced slips over the 3 1/2 years that the base has been operating. I would say almost everyone has been involved with one, it was particularly bad when there were the issues with the engineers and their EBA.
Qantas sop is to try blackmail. Ops would say that they will give you a longer slip in Lax, say 60hrs but will send you home via AKL or MEL and therefore you will lose your next trip.
Then they will offer reduced slip allowance to sweeten the deal.
I would guess that 95% of the time the crew will chose to take a reduced slip, it's no big deal and generally only a case of 4 hrs or so, and doesn't stuff up your plans at home too much.
For Brisbane based crew it's all about lifestyle.