For most organizations today, this is the best of all three worlds.
The forum is for responses to new and unique questions.
The knowledge area for documenting the new responses and tackling the most common questions before people call the call center.
The ideas area for product complaints and suggestions (because isn’t every complaint also a very precise suggestion?)
Once you realize what each area is for you can begin to optimize each.
The goal of the forum is to answer the question in the quickest possible time and with a satisfactory answer. That means immediate access to experts who are eager to help and know what they are doing. This, in turn, means growing a base of experts who are motivated to answer questions.
The goal of the knowledge base is to hit the search traffic for the most relevant terms. This means keeping it frequently updated and ensuring it’s technically suited for search. This means finding processes to highlight the best material and the people who enjoy documenting this knowledge.
The goal of the ideas (or complaints/customer service) zone is to respond to criticisms or complaints where people feel listened to and that they had an impact. You might want to use a Reddit-style ranking feature for this so people can vote up the ones most relevant to you and surface useful insights from the community.