I think that they are helpful, but not absolutely necessary. I think that some people will be weary to post on the forums, so there needs to be other options available, as others have mentioned. Also, the forum would have to be populated, and should show that others with problems have been helped.
AbbieRose also makes a good point - there are plenty of forums out there that help might be offered. Some of your clients will flock to the bigger and more popular forums, but some might actually prefer a very personal one that is only for clients or potential clients.