The choice between selling ads directly and using Ad Networks can play a huge role in determining how much money you can earn. 

I want you to think about your website as a piece of online property. A digital plot of land you own and control. 

The easiest way to make money from this piece of land is to pay a firm to connect you with buyers interested in buying renting this “land” from you. This is similar to using ad networks like Google AdSense or Yahoo ads.

However, imagine how much more money you would make if you instead took that same piece of land and built an apartment complex. Then, you sold or rented out the individual units. It is a lot more difficult, but you would also earn a lot more money! 

This loose example illustrates the difference between doing direct ad sales and using an ad network.