Forums are generally topic specific communities where people with a common interest can help each other and discuss topics related to the forums theme.
On WebmasterWorld we discus everything related to web development. Its not just one way help. If you see a post that you think you can answer, please feel free to do so. That's the amazing thing about this site, many members have been here for years. At first they are new to the industry, now they are regularly helping the next generation of webmasters.
None unless you do so for the right reasons. :)