File this under "I've just noticed - is this new?"
Google is asking searchers whether they want to block all ads from a domain. For a while now Google has been offering to block natural search results for a domain and this PPC version is exactly the same.
If a user searchers, clicks and then returns to search again without hanging around on the site then Google prompt for a decision. In my case I wanted to see whether Netflix had Game of Thrones. The site doesn't tell me so I bounced off.
It's certainly interesting. You would have to figure this feature impacts quality score - and perhaps SEO signals too.