You can sell you advice and knowledge to many people. You don’t have to be super expert in one domain to become a consultant or teacher, you just have to be better than your student or client. Anyone with a core competitive skill can become a consultant and find clients online. For example, if you are a legal or finance professional, then you can make your website, and start attracting clients online.
Niche marketing can be extremely cost-effective. For instance, imagine you offer a product or service that's just right for a select demographic or ethnic group in your area, such as Hispanics or Asians. You could advertise on ethnic radio stations, which have considerably lower rates than stations that program for broader audiences. So your marketing budget would go a lot further, allowing you to advertise with greater frequency or to use a more comprehensive media mix.
Unlike mass audiences, which represent a large number of people, a niche audience is an influential smaller audience. In television, technology and many industrial practices changed with the post-network era, and niche audiences are now in much greater control of what they watch. In this context of greater viewer control, television networks and production companies are trying to discover ways to profit through new scheduling, new shows, and relying on syndication. This practice of "narrowcasting" also allows advertisers to have a more direct audience for their messages.