Why would you block an ad on your site? Maybe your family-friendly business is disinterested in ads for escort services; or your right-leaning blog is no place for left-leaning campaign ads. Or, you wish to block ads from a particular company because you already have a direct advertising deal from it. Or, you want to block ads from a competitor.

All well and good, but Google in its AdSense blog offers some practicalities. Ad blocking "shouldn’t be thought of as a means of account optimization," it advises, just as a way to be sure you are satisfied with the ads shown. But, ad blocking should be used sparingly: displaying all ads creates the most competitive atmosphere in the ad auction, with the largest inventory possible competing for an impression on your site.

Some of the practicalities:

• Blocking low-paying ads does not ensure that you make more money. Even if an ad contributes just a small portion to your revenue, blocking it will likely cause a lower revenue-generating ad to show. Google will always display the highest-paying ad, so an ad that appeared on your site was the highest-performing ad of all available.
• You may block some ads and see revenues rise, but, that lift is not sustainable. Earnings in AdSense fluctuate, constantly. Revenues depend on a number of variables, including traffic to your site and advertisers changing bids. Google targets target ads based on content and audience—so, the ads you see are not necessarily the ones users see (e.g., interest-based advertising and geotargeting). Also, ads that seem off-topic to you as a publisher might in fact be the most valuable to the user in that browsing session.
• Blocking more ads is not a way to "fine tune" the ads on your site. The ads that win in the auction are ones expected to deliver you the most revenue, while ensuring a good user experience. The same ads do not always appear on your site for a variety of reasons, ranging from changes in advertiser spend and advertiser preferences to geotargeting of users.