When I flew 727s the only time the forward baggage heat valve switch would be closed would be for a pressurization problem in the cabin and one needed additional bleed air for the cabin. All other times it was left on during normal operation.
The '72's that I flew were old 200's, used and from many sources. Engines ranged from Pratt JT8D-7's to -17R's (sometimes mixed
). Manual and automatic pressurization.
I think the old manual pressurization planes had the worst door seals. You had to be ready with the cargo heat outflow switch, or sometimes leave a little power on in the descent with the speedbrake out a bit, to maintain pressurization on the way down.
The switch on the FE's panel was called the puppy snuffer switch.
Yep, I hesitated to mention that fact in these times of heightened sensitivity and PETA protests.