My CCKW manual (1944) says basically the same thing: "in cold weather"... "aid in vaporization"

http://www.tm9-801.com/searchTM9/tm9_pages/261.pdf

But on that 270 the operation is entirely MANUAL. No thermostatic spring... just ON, OFF, or 'Best Guess'

http://www.tm9-801.com/searchTM9/tm9_pages/264.pdf

So I can't believe that it is a super critical item. More like 'it kinda helps more than if it weren't there' kinda deal.

Fuel injected motors (even old TBI) didn't use it.. and the fuel coming out of the injector was not a vapor, just atomized.