The Notification Center to makes it easier for you to get work done. When you click on the Notification Center icon from the global header, you can see when steps have been assigned to you, when people have mentioned you in comments and more. And, if you have notifications from other instances, you can navigate to the other instance, directly from the message!
You have the option to choose to receiving notifications via email or in-app. And even better, you can fine tune the types of messages you want to receive under My Settings.