YouTube playlists are mostly used by people to, well, play music. Apart from that, they are also great for learning and teaching. Its easy to create and share playlists (using the my videos section on YouTube). But few people know that you can also easily embed them on blogs or on Moodle (see image).
This is particularly useful if a video has got several parts (due to the duration restriction of 15min, or even 10 min. until recently) or if there is a series of videos on a particular subject. I teach a CLIL project management class and I keep a playlist which is exclusively about project management vocabulary.
Using the embed code I can easily embed the whole series in moodle and the students never have to look for the single parts in different places. The embedded player has an additional button which allows you you display the playlist. Very slick and clean.
Using playlists allows you to make video collections of subjects and classes for future reference. So when students want to revise they have quick access to that video as well as a teacher for classroom use. This is particularly efficient in combination with the YouTube remote control app.