At the bottom of every piece of content, you have the option to "Upvote" or "Downvote" the content. Your answers are private, they are never displayed, and the Author will not see this. But this information helps Harvest's Recommendation Engine get smarter so that it can serve you content that is most relevant to you.
If you hit the Thumbs Up icon on a post, you are signaling to Harvest that you are interested in this content. Recommending a post does not mean you agree or disagree with the thesis, not does it mean that you are endorsing the author or his/her thoughts. You are simply alerting Harvest that the post is worth reading so we can curate your feed with related content in the future.
Similarly, the Thumbs Down icon sends the opposite message to Harvest.