Of the 9 staple AdWords extensions, sitelinks are among the most effective for ecommerce businesses. They funnel shoppers to targeted pages on your site and consume more valuable ad real estate. Now AdWords advertisers have the luxury of populating their ads with dynamic sitelinks – “automatically generated sitelinks that appear below your ad text, connecting potential customers to relevant pages on your website more easily.”
The best part about this is that clicks on dynamic sitelinks are free. Google will automatically populate your ads with dynamic sitelinks if they interpret a specific query may be best matched with a page on your site.
The key thing to keep in mind here is that these won’t replace the current sitelinks you may be running, nor should this introduction stop you from manually adding sitelinks in the future. This is because A) you still want to add sitelinks you know are relevant to specific ads and B) dynamic sitelinks will apparently not see very much impressions.
You can choose to opt-out here.