The Notifications section is where you can see all your account activity, whether someone has mentioned you or a video has been posted for you.
It is a quick way for you to get to those important messages and clips you have been tagged in with ease. Also, if you remember a great clip of yours from a while ago, it's an easy spot for you to scroll back and find it. It's like your collapsed version of your Feed.
One point to note here is that the notifications will only show the team that you are currently logged in as. To check the notifications of the other feed, just switch over to another team in the Menu.