Before now, enabling notifications within the YouTube app would only result in an Android device getting alerted whenever the app had something new to report. Now, there's a tab in the sidebar that's dedicated entirely to these messages. Users can click on it to view their notification history, which should make it much easier to flick away future alerts without wondering if that action will be regretted later.
Notifications will presumably still pop up as before, they just now have a place to stay after they've been dismissed. For the sake of comparison, here is how YouTube's sidebar looks sans notification tab.
As you can see from the pictures above, Artem already has the tab. He isn't alone. Nevertheless, it has yet to pop up on any of my devices. The change is being toggled server-side, so if you don't see it yet either, try to wait it out. Though it probably won't hurt to have the latest version installed, just in case.
Thanks, Lee Jarratt