I notice you ignore the comment about whether or not you actually intend to handle the snake...
The thing is you don't know exactly what does and does not stress a snake unless you're Voldemort.
HOWEVER; animals have seeking behaviors they display when their needs are not being met. This can be hunting, looking for a hiding spot, ect. Any behavior that meets the animal's needs. If the need is not being met, it will seek it out. When a BP has all its needs met (including safety) it will stay hidden in one spot until it gets hungry (need not met).
Being handled by a human is something that stresses snakes because it removes one of those basic needs; the need for somewhere to hide from predators. This is why your snake will typically move around while you handle it rather than just curling up and going to sleep. Sometimes it will ball up which is also a defensive reaction.
The reason you want to avoid this after a regurge is because you don't KNOW exactly when the snake has stopped being stressed by the event, and it is far better to overshoot than undershoot and end up causing more problems by adding stress.
That, and it's common sense that being handled by a giant monster is stressful to something with the mental capabilities of a snake.
Seeking behavior is a common-knowledge sort of thing with far too many scientific articles to sift through, so rather than giving you a scientific article I'll just say that Temple Grandin's "Animals Make Us Human" is an excellent casual read on the subject.