John in NM
That makes more sense than my explanation. One trouble with this stuff is that it is less than obvious to us casual users. The tricky part is remembering the expert explanations later

In the case of filling large voids using something like West System, if you have problems with cracking or boiling, using a short measure of the hardener will avoid those problems. While the advice is less than ideal in many respects, but in a production shop it is a reasonable substitute. Usually management doesn't want to wait for the proper product to be found and purchased, you don't want to waste lots of time filling little bubbles or cracks later, and the hardener reduction did not seem to be too detrimental in practice.

Having since used some very fast and hot urethane resins, I think that "boiling" could instead have been absorbed water coming out when it got too hot. The urethane resins got that hot regardless so you had to be very careful to use new, clean, plastic mixing cups, but I only recall West getting really hot in large, bulky shaped pours.