This is nothing new. Since some time, Google is showing answers in the search results page itself. And now they are prompting webmasters to mark the best answer in a discussion. Hopefully, that will end up in Google search result page as an answer to the query.
It is helpful to the end-user when you are looking for something. There will be a topic with lots of replies and the user gets confused. Once you have a best answer mark, it is quite easy for them to identify the answer.
What is your take as a webmaster on this SEO trick ?