You also have to remember that running anything from a home based PC will eat up your bandwidth if you run it as a server. Which means that you will have less bandwidth to use for your PC. So turning your PC into a server which will make that PC useless to you since it will be under constant load (Server purposes) you will need a 2nd PC. Which wil be rendered useless to the internet since your internet will be eaten all up by the server you created.
Plus you also haev to realize that if you host a site or something from your home based PC and someone wants a file or something from it then you are also limited to home many people can connect to the Server at that time. Cause you are limited by your upload speed. So if you upload speed is being taken up by someone downloading a file then that means someone else cant load up your stuff cause you can physically upload any more.
That is why servers are done on bandwidth lines that can handle more of a load than regular ISP's will provide. While any PC can be turned into a Server. It is you ISP and your bandwidth that limit many people from running servers from their home.