This is an additional line of information that can be shown with text ads to highlight important information for searchers — the ultimate goal being to encourage more click-throughs.
Google has now doubled the amount of structured information that can be shown with text ads, giving advertiser’s an additional line of structured information to work with.
This can be accomplished through selecting two predefined “Headers” — which serve as your structured snippets — and then customizing those headers with two sets of values. The two sets of information now have the possibility of being displayed at the same time.
As one example, this could be useful for service providers wanting to highlight their most popular services, as well as the top brands they work with.
Google reminds that each structured snippet extension is subject to its own ad auction and, like other ad extensions, may not always be shown together.
You can improve the probability of having both extensions show at the same time by providing as much information as you can. With more information the ad auction is able to better select the best combination of extensions to show to boost enhance performance.[“source-searchenginejournal”]