Article: YouTube offers users the ability to view its videos on web pages outside their website. Each YouTube video is accompanied by a piece of HTML that can be used to embed it on any page on the Web. This functionality is often used to embed YouTube videos in social networking pages and blogs. Users wishing to post a video discussing, inspired by or related to another user's video are able to make a "video response". On August 27, 2013, YouTube announced that it would remove video responses for being an underused feature. Embedding, rating, commenting and response posting can be disabled by the video owner.

Now answer this question: What is the most common use of embedded youtube videos?
social networking pages and blogs