Apple statement:
"Apple believes that people have a right to privacy - Safari was the first browser to block third party cookies by default and Intelligent Tracking Prevention is a more advanced method for protecting user privacy," Apple said. "Ad tracking technology has become so pervasive that it is possible for ad tracking companies to recreate the majority of a person's web browsing history. This information is collected without permission and is used for ad re-targeting, which is how ads follow people around the Internet. The new Intelligent Tracking Prevention feature detects and eliminates cookies and other data used for this cross-site tracking, which means it helps keep a person's browsing private. The feature does not block ads or interfere with legitimate tracking on the sites that people actually click on and visit. Cookies for sites that you interact with function as designed, and ads placed by web publishers will appear normally."
http://appleinsider.com/articles/17/09/15/apple-addresses-ad-industry-complaints-over-safari-tracking-prevention-feature