I have found that YouTube has a wealth of potential for student learning. This clip I found demonstrates the volleyball bump and set, 2 skills that I just finished teaching in my own classes. If students are having difficulty or are absent for a day, I can find a video and refer them to that so they can see some of the content and demonstrations that were taught in class. This can allow them to stay up to date if they are out, or give them pointers when they are at home as a review.
However, as many of us who have been on YouTube know, there is tons of videos that students should not be watching. It is a difficult task to try to monitor their usage especially if they are being asked to watch a clip on YouTube from a home computer. There is no way of making sure the students do not venture off to other videos after they watch what you have asked them to, but there definitely is a use for the clips as an educational tool.