And it's not just when on business.

If I fly from London to Sydney for a holiday, I can take a day flight, which "costs" me two days and one night and dumps me in Sydney knackered from having been awake on the whole of the long first sector and getting only a few hours sleep on the second sector.

If I take a night flight, it "costs" me two nights and one day, and I can arrive in Sydney after having slept most of the long first sector and then getting another few hours' nap in on the second sector, and thus ready to hit the ground running.

On that basis, the choice of a night flight is really a no-brainer. (Of course, if upgraded I have been known to wreck my opportunity by staying up to sample the service.)