The folks over at YouTube have recommended that all channels have some kind of a channel trailer introducing their channel to new viewers. While in some ways this seems a little bit silly, it makes sense. I have no idea how many channels there are on YouTube, but it's probably in the hundreds of thousands, if not the millions, and so there is a lot of content available on YouTube for viewers to watch. People with YouTube accounts can decide to subscribe to as many channels as they want and this helps them to keep up with new videos released by channels they find interesting. It is recommended that all trailers contain a "call to action" requesting that viewers subscribe. This is considered a step along the road to building an audience and what's the point of making videos unless people actually watch them?