Trackable, if you really track (Score 1)

This is the same issue that direct marketers have dealt with for years, just in a new outfit. Unless you can track down to "paid-for sales", and then accurately derive the total value of that sale (after all the associated costs of making the sale, advertising included), you know *nothing* about the effectiveness of your advertising. After 20 years of experience with so-called marketing experts, I can say for certain that most do not put in the effort to know what marketing is working for them, and what is just sucking up the money. Once you track to the total profit from each of your sources, the claimed impressions is irrelevant. Some exceptions are tied to branding and building product awareness - you may be willing to lose moeny to sway an influential niche market - but you should still know how much money that costs. Most have no idea.