I think it's more like coming up with heuristics to approximate an answer quicky, even if the answer is wrong . With option trading, being able to intuit what the option should be priced at.

Option trading was my first thought too. I went on a tour of the CBOE years ago with some former pit traders and they setup a mock scenario as if we were in the pits during an active trading day, to teach us how all that worked. I was thoroughly impressed by the ability these guys had to do all this math in their head, and maintain the bottom line of a complex position, all while surrounded by chaos.