A group of advertisers have requested Apple to rethink/withdraw the release of Safari 11 in MacOS 10.13 (High Sierra) and iOS 11 because it contains an Intelligent Tracking Provision that blocks cross site tracking. You can read Apple's response in this MacRumors article.

If this were a MacOS only feature the battle would be pretty one sided but since it also appears in iOS, the odds would seem to favor Apple. It will be interesting to watch how this plays out.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein