if threads digress as widely as this one has from the original subject line, is it customary to start a new thread?

The Committee for the Preservation of Thread Purity long ago recommended a rule which required one going off on tangents to start a new thread. The problem was that, in the thread in which the new rule was proposed, one poster took off on a pun about geometry and that subthread ended up talking about the origins of that academic study in Ancient Egypt. And another poster took off on how a term (thread) meaning fiber could be used in the context of organizing thought. By the end of the "thread", nobody remembered where it started, very much like conversations at cocktail parties.