How does P2P work for me?

Peer to Peer networks could work for an individual in many ways. My personal example being is that a couple summers ago I wanted to create a server for the popular video game "World of Warcraft" in which I could have a bunch of my friends play on this private server without paying a cent for the actual subscription WoW charges it's users. Now my server knowledge was still in its infancy at best, so I actually had set up a very basic p2p "ad-hok" network in which the server was treated almost as like a LAN party where ONLY my friend could log in, not allowing for just anyone to sign up on the website and make an account (that would come later) Using the popular adhok program, hamachi I set up the network relatively quickly, and got my friends to install the hamachi clients on their computers so that they would be recognized and be able to join the network. I believe at the time the most people my network could hold at the time was something like 15 people, (though it seemed like 1000) setting up a basic p2p network like that is what got me into networks in the first place.