If these are lead generating ads, you could determine if a click lead to a sale. If you had this data (which was pointed out by the OP about tracking every click - although he insinuated its bad), you could determine what types of ads work and which ones don't.

So this is two fold, you remove the ads that don't work (so you don't annoy your audience), which in turn creates a more potent advertising experience for vendors which makes that real estate more attractive.

The trick is not letting every dog through the door and keeping some class.