(1) You can keep your username, and it won't be linked to your profile. (You get a Google+ page instead.) (2) You don't have to have a channel at all if you ju

(1) You can keep your username, and it won't be linked to your profile. (You get a Google+ page instead.) (2) You don't have to have a channel at all if you just want to watch videos, subscribe, etc. But you do if you want to create playlists, even private ones. Your channel has privacy settings so you can hide everything. But if you don't trust YouTube to keep them hidden, then you probably shouldn't use it.