A briefing on this new branding feature in YouTube's "One Channel"
Viewers who are yet to subscribe to your YouTube channel and visit your channel page, can now be greeted by a video telling them why they should hit the subscribe button. This is an opportunity to show these potential subscribers what you do, and why they should sign up.
This new feature is just one part of the new “One Channel’ design that YouTube started rolling out in March 2013. The core benefit of this new design is that your channel will have a uniform look across devices. Other useful features include the ability to create playlists and the ability to link to associated channels straight from your channel homepage. The most exciting feature, as far as creativity goes, is definitely the trailer feature. Here's one nice example of a channel featuring it: