Certainly YouTube has a lot of features, that gets new addition quite often. And sadly, not everybody knows about them. YouTube has now launched a new service dubbed 'Adopt a Feature' to promote less popular features via its community. YouTube has similiar section for YouTube Help Center.
Here’s how it works: Select one or more features from the list, make a video about the feature using the precise tags, as indicated for each feature.
Demo: LisaNova’s video about subscriptions