Notification center allows to review your work-related notifications.
All the new (unread) messages get to this section. Once reviewed, you can close them or leave in NC for further interaction.
You can also review the following events in the Notification center: new processes, notifications left in processes where a user is an observer, emails, change of status in the process.
You can use this section just to view the new messages, or move to process from there or open email from Notification center and work with it further.