All reactions are an equilibrium. It just depends how far and on which side. Removing a product as it forms will drive a reaction. See Le Chatlier’s
principle.
Everyone is saying that vacuum doesn’t seem to speed it up, so the rate isn’t largely effect I guess. I’d bet you decarbing is sped up even if just a little bit though.
I think the biggest advantage however as some people have pointed out is that you remove oxygen. Heat + oxygen + time = cbn or other isomer. If you can decarb under vacuum or inert gas, that would be ideal as far as preventing degradation goes.
I’ve seen some graphs that illustrate why you shouldn’t decarb hot with oxygen. I’ll post them tomorrow if I can find them.