I don't know why it took me so long to think about this, but if you ran a site that has generally high CPM rates (from different advertisers combined) of over $1.50 CPM ..
Would you spend money on Advertising to keep increasing the flow, if so...from where would you Advertise from ?
We don't sell anything on our site, just mostly an information / news site. But could definitely use a hit increase.
I'm guessing it would have to be good quality (but cheap priced) advertising...otherwise it could lower our CPM rate in the long haul.