asian eagle may have been alluding to the fact that with one crew of four you have one lot of descretion on those patterns with very little spare time.
in the past with two sets of crew e.g.. two captains and two FOs (Hkg-Dac-Han-Hkg) they were on the same aircraft but operating on different duty times, and both had discretion independent of each other.
Thats what scheduling hoped.