The latest rediculous one came from a chap who saw nothing wrong with leaving the apu bleed on with packs switched off on the ground (737NG). I can’t recall if there is mechanical risk to apu health in this config, but I do know that it results in approx 40% loss of efficiency, half that (20%) if only one pack is used for the 131-9b on 737ng, (off the top of my head); I can’t remember where I read it so I wouldn’t be able to produce evidence even if I tried! Hah.
Sorry for hijacking...
What about having packs off and APU bleed on? With or without APU running? 8 years now on the 737NG and I thought I had pinned down the essentials.