http://www.redditsecrets.com/ should answer most of your questions of what these are great for. Excellent for marketing, great for buying and selling on reddit, aged high karma accounts you can typically post anywhere on reddit without hitting any of their filters. If you run a company, this is an excellent way to bring in sales and improve your SEO ratings from articles you release. If you are an affiliate you can make money from cpa offers, those are just a few of the many uses of these accounts. Hopefully I cleared that up for you!