Most Github repositories I'm aware of use the following workflow for pull requests: one or several users with "contributor" privilege review the suggested changes and then one of them merges the pull request which most of the time requires just two clicks - "merge" and then "confirm merge". Here's an example in CoreFX repo - one of contributors merged the changes.
However there's OpenCV repository with pull requests like this where one of the contributors reviews the changes and then approves them by posting a "thumbs up!" comment which causes a dedicated user opencv-pushbot to merge the changes. It looks like no contributor ever merges the changes himself in that repository - they are all merged by the "push bot" user.
What's the use of that? It takes the same amount of labor to post a "thumbs up" comment as it takes to merge the pull request. It also makes it a bit harder to track who approved which merge because now all changes are merged by the same user.
What advantages does the "push bot" approach have?