I guess it depends on too many variables, including maintenance 'deals' for APUs. E.G. In DanAir 737s, we were switching the APU off after start and lighting it on landing (as per SOPs) on LGW-CDG and LGW-BRU sectors (of which we flew many daily) and it was determined that the 'hot cycling' of the APU had a negative effect on service scheduling. We left it running for the 28 mins or so and APU serviceability apparently went up. It is the same deliberation as to whether brakes or reverse are cheaper on landing.