The goal is not exposure, unless you are talking about the content network and not search. Even then, you don't want purely exposure, you want clicks. First because clicks improve your QS which reduces your CPC. Second, because the purpose of advertising is to get people to your store. In the case of PPC, to your site. If they don't click, it means they are not interested and exposure is not going to change that and improve your bottom line. It would be like putting an ad in a newspaper and nobody called or came to your business. You'd get exposure but what did that get you? It means nothing if you can't generate revenues.