Some of my sites have ads on them and some do not, it all depends on many different factors. When I first create a website or blog I usually won't have any advertisements on that site in hopes of gaining a regular following of visitors/readers. Nobody wants to go to a new site and the first thing that they will notice are advertisements.
It also depends on the type of site that will determine if I have advertisements on them of not. Some types of sites like forums for example need to have some source of income to cover the costs of hosting, software and everything else that goes along with a forum in order to keep it free for anyone to use and benefit from.
I don't really have anything set in stone as far as I am going to have advertisements or not on a blog usually as there are other ways to help make money with them.
It all depends on many different factors in deciding if I am going to have ads on any given site of mine.
