This is usually used in quizzes and other such polls where people will be asked to choose one or the other. This is a smart way that allows users to easily signify what their choice is.
The idea of choice is one that is increasing on social media platforms; people are able to decide on liking or even disliking something. It is essentially a part of a democracy and allows people to decide on what is good or bad. This in turn pushes things up to be more apparent and allows things that more people like to come through.
The web is very democratic in many ways and the more popular something is, the higher its rankings are on Google in most cases. This is one of the web's greatest benefits and one of the best things about it.
Being able to see how many likes or votes something attracts can also be a good personal gauge to whether you will spend time looking at it and that it is not a waste of time.