Google is soon releasing a new system where ad landing pages will be automatically spidered by a new AdsBot. The content of landing pages will help determine the quality of an ad campaign. The ad's rank will be decided bya combination of this quality score and the amount you are willing to pay. It will also be the major factor in deciding where your ad will be placed.  A high quality score means you can rank higher even if you pay less than others. If you choose not to participate in the new spidering system, you might hurt your AdRank.