Ideling an engine too long without use of fan

[AirGsPd]

I have read a lot that you should not let your engine idle longer than a few minutes without the use of a fan. I do understand the concept and thought behind that advice , but here comes my question. Have the engines not been designed to withstand ideling for a longer period of time like it may occur in a traffic jam? What are you guys doing if you come to a standstill somewhere on the highway?