A forum lets you better communicate and interact with site visitors while generating copious amounts of relevant content. This, in turn, makes you rank higher for the search engines. A forum can be a place where your visitors can discuss products and services or where you give comprehensive responses when questions aren't being answered.
Allow users to post questions- reduces demand on customer service team and can allow a moderator to quickly deal with problems or demands before they get out of hand.
Optimizes for search engines- the content created gives a great place with constantly updated information which should be full of keywords the engines will scan. This also creates your site as an information hub for the engines.
Evaluate customer feedback- great place to understand what your business is doing well and how you can improve on whats not.
Conduct contests and give-aways- this will generate more traffic to you forum and also more participation. The give-aways can be something to promote your products too.
Dedicate time and resources- all that is needed is an employee to serve as a moderator who can continuously monitor the forum for problems and inappropriate content.
Set rules- you need to have set rules in your forum not to let the users get out of hand. These rules could be as easy as not letting others advertise their product to not allowing links to be followed from your site.