Uncle Bob's insistence that functions should be 2-4 lines long is baffling to me. I don't understand how he can be taken seriously. Is there a single application in the entire world with substantial functionality that conforms to this rule?
However, a friend of mine was a professional Smalltalk programmer. He claims that his median line count of methods, over his 17 year career, was 4.
It is harder to do in other languages--it seems that C would be on the order of 10.
Clearly it is a rule that can lead to complexity of too many methods, compromising whatever gain smaller methods give you.