The website owners  earn money from the  advertising on the website but forum members are expected to contribute  without any benefit.  Such websites are best avoided.

Some of the advantages of posting in popular high traffic forums are:
1. The internet is constantly changing and forums are often the first place where new ideas are posted. By posting or lurking in forums, an internet marketer remains updated on the latest trends.
2. The best selling products / services are those for which there is a lot of demand. New products / services can be developed by studying the demand for a particular product.
3. By posting in relevant forums, the marketer can reach the target market, who will visit their website for more information.
4. Making useful posts helps in building trust and credibility
5. Signature links can be used to promote products and services, which can be indirectly promoted in the posts . However, different forums have different rules regarding signature links and care should be taken to follow them.
6. Many search engines rank forums high in their search results, and posting can help the website get ranked in search engines.

Like any business, it is usually some time before an online business breaks even. The time taken to break even depends to a great extent on the product selected, profit margin  and the marketing expenses. If the business owner has some free time, he or she can use the various free internet advertising options available.  These can be very effective, but are time consuming.
The other option for getting visitors to a website is using PPC (Pay Per Click) programs, but these campaigns are often very expensive for newcomers.

To earn money from a website, it is important to get targetted traffic. There are many programs that promise to send thousands of visitors to a website for a low price, but many of these “visitors” are actually bots or participants in Paid to Click schemes. It is important to measure  the conversion rate for different types of traffic and only try to get traffic which converts well.