I am just about to launch my site. I am launching it completely ad free. I am doing this for a few reasons. First, the site looks cleaner. Second, people may be more inclined to use the site if there aren't flashing ads coming at them. Third, who would advertise on a site with little traffic.
My question is, what would be a good benchmark for traffic to a site before I should start putting ads on the site. 100 view per month seems really low, 1,000,000 seems really high. Is there any links to studies, companies requirements, personal experiences you can recommend?
I would address your question from a different perspective. I agree that without ads your site looks cleaner and more people will likely use it, but this has a cost for you. It is the missing advertising revenues.
So your question could be: how much am I willing to pay for a cleaner site? Calculating (roughly) your missing revenues is not very difficult. Let's say that you would be getting 0.1$ for every click and that the CTR would be 1% (so that 1 every 100 unique visitors clicks an ad).
With these assumptions you are loosing 1$ in revenues for every 1000 unique visitors.
You might want to play with the numbers, but my advice is to define a budget and start introducing ads when you believe the missing revenues are worth it.