Some people say that it helps ensure the post shows up on your friends’ newsfeeds. As you may know, Facebook selectively fills the newsfeed with your friends’ posts. Not every status update is shown. One of the criteria Facebook uses is the number of likes a post has. By liking your own post, you add one more ‘like’, which may mean Facebook is more likely to put it in the newsfeed. I’ve just heard this anecdotally, so I’m not sure if it’s actually true or not.