Being a contributor on various forums, I know the importance of posting answers to the questions. According to me, it's important for both the OP and the one who answers. I see people with over 50K reputation here on this forum and felt asking this question.
Welcome to The Workplace SE. As others have mentioned, we're not a traditional forum. Instead, we're a Questions and Answers site. The major difference is the focus on answers, not discussion, and the result is a wealth of knowledge, without the noise generated by discussion, which can be searched from major search engines.
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The biggest benefit you'll get by contributing answers is that you'll learn. Answering questions will force you to think about the problem on a much deeper level and formulate an intelligent, quality answer which will last for years to come, helping future visitors to the site. Hope this helps.
As far as I know, there is no site to highlight your contributions to Workplace SE, but I imagine one could experiment with putting this in their CV or resumé, if it's applicable to the job they're applying for.
In addition to forcing you to think harder and formulate your ideas(as jmort mentioned), I enjoy helping people.
If I can provide a good answer to an question, I have potentially helped the asker and any future person who finds that answer later.
I would certainly consider including my workplace.se account on my resume when applying for management type jobs. Similar to how many developers include their stack overflow accounts. I think it would give a potential employer a lot of insight into my management style, writing ability, communication skills, judgement, etc.
