I don't think there's a right answer to this so I'll just tell you what I do.
I consider help.u.c and the official documentation to be like a library. There's a breadth of knowledge there, but there's really no way for you to ask someone "Hey, so in this section of the DNS manual, why do I need to specify foo here instead of here?" and so on.
So in an ideal world think of official documentation as textbooks. Sure, there's info there, but man it can get dry pretty quickly. I can't think of anyone who sits down and is like "I cannot wait to crack open a beer and dig into these manpages tonight."
That's where AU comes in. If documentation is the textbook then Ask Ubuntu is your study group, the kind of place where you can ask people to clarify things you don't understand. The FAQ states:
Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.
So, if someone is asking a question and your answer is to link to an entire chapter of the Ubuntu wiki, then likely the question is terrible and offtopic and needs to be rescoped. We're here to answer people's specific questions about a topic, not replace wikipedia.
Since the best answers always include references, in an ideal world I see the perfect answer answering a question about something, but then including references to the sources, but also highlighting the obvious answer so the next person doesn't have to sift through piles of dry text to find the exact answer they need. This is crucially important, and it's why answers like "here's the link to this forum thread" is frowned upon. Don't make me read a 5 page thread of stuff to sift through, I want the answer to the question ON TOP, right away!
People who ask great questions aren't looking for a just a link to documentation (any idiot can search on google), they want and expect thoroughly detailed answers from subject matter experts on the topic. These are things that supplementary to the the official documentation, like experience, opinions on best practice on how to solve a problem, and most importantly, the response from a human being to your exact problem, using the documentation as a reference.