[henrik_w]

I agree, that's an excellent reason to create a function/method. Reason 7, self-documenting code: http://henrikwarne.com/2013/08/31/7-ways-more-methods-can-im... (but of course it doesn't mean that you never need comments)

[goblin89]

I think it's said that you should document the "why" (as opposed to "what"), which is relevant when you're using an unconventional approach or for some other reason your code may not be understood immediately, or when business logic is involved.