I think forums help all websites especially any that give a service of any sort. Different sites have different goals but usually making money is one of the main ones.
We have them on our retail sites - when one stopped working a few months ago I didn't think much of it. But have since had a couple of emails asking for the forum to be put back online and pointing out that they visit the website less often (and therefore buy less) since the forum stopped.
I don't think I would have revisited this site so often without the forum - I would then have not got my free domain name and some cheap hosting

. But I also would not know about any new offers and be less likely to come back here for more hosting.
You can also see in forums how they deal with complaints or problems - assuming they don't edit or delete threads
