In many cases, there may be unread documents in a database that are unimportant to a user and others that are important. A simple example is the mail database, where I would like to see the unread count for the Inbox only to show in the workspace as unread. Inside a different view, you could still see unread documents, but as a user, the unread from the Inbox is what is important.
Any number of other databases would be more effective with this feature. A bug reporting database might have the view set to Open Bugs. A product database might have it set to current products. With this feature, a user could easily glance at the workspace and see where action might be required without getting confused by hidden or irrelevant unread documents.