Most of the major reasons can be found on the home page forum "in the shade", password rcia. Read the post on new forum rules. There are numerous benefits to being a premium member relating to what and where you can post, which plays a big role in developing SEO for your business. Info flows more freely in the premium section due to other members seeing that you are serious about building a business and helping to support RCIA. If you are serious, Premium is where its at.
There may be so small cons involved ($100.00 fee), but if you receive several thousand $$$ worth of internet SEO, it is probably worth it. LOL