Ad Extensions make your PPC ads stand out and they also offer users more options, so it’s no surprise that they increase CTRs and interaction with ads. Some examples of extensions are click to call phone numbers in mobile ads, sitelink extensions and offer extensions, which give users printable coupon for offline use. Studies show that things that don’t match stand out to people (like a sweater and a bathing suit, or so my friends keep telling me) so if you’re using Ad Extensions, your ads are more likely to be noticed and clicked on.
Extensions don’t cost anything extra*, and since they traditionally do increase CTRs, it’s possible that Google automatically bumps up your Quality Score when you use them. Google plays it pretty close to the vest about how scores are calculated, so this is speculation based on what they have admitted. However, even if they don’t automatically factor in the use of Ad Extensions, extensions do improve CTR, which means you’re likely to get the score boost either way.
There are no additional charges for extensions right now, but you’ll still pay for a click if someone uses the click to call feature or clicks on a sitelink instead of the main ad.