Youtube has been the most common location to share videos especially when it comes to shared knowledge like how to do this and that. While most are already connected to the internet via DSL (unlimited connection), there are other who are without connection at all or their connection is bad (slow). Replaying the videos, especially if they are teaching something, are vital in learning, which means they need the youtube download in order to be able to play them over and over without having to reload it through the internet over and over again. Different operating systems render downloading also differently.