I do not find this to be the biggest value-contributor amongst my spontaneous conversations. I don't have a good hypothesis for why spontaneous-ish conversations can end up being valuable to me so frequently. I have a vague intuition that it might be an expression of the same phenomenon that makes slack and playfulness in research and internet browsing very valuable for me.

One of the directions im currently most excited about (modern control theory through algebraic analysis) I learned about while idly chitchatting with a colleague at lunch about old school cybernetics. We were both confused why it was such a big deal in the 50s and 60s then basically died. A stranger at the table had overheard our conversation and immediately started ranting to us about the history of cybernetics and modern methods of control theory. Turns out that control theory has developed far beyond whay people did in the 60s but names, techniques, methods have changed and this guy was one of the world experts. I wouldn't have known to ask him because the guy's specialization on the face of it had nothing to do with control theory.