For various reasons, there are times when an administrator does not want a part of the ECP to be accessible by some users and they desire a features' tab or entry point to not be visible at all. The web.config file for the Exchange Control Panel (ECP) contains the requirements a logged in user must meet before the feature tab or configuration item may be displayed in the UI. In Exchange 2010, Role Based Access Control (RBAC) is the new permissions model that allows you to assign granular permissions based on management roles. To learn more about RBAC, see Understanding Role Based Access Control in Exchange 2010 documentation, and the previous post RBAC and the Triangle of Power. In Exchange 2010, the Delivery Reports tab in ECP allows users to retrieve delivery reports for messages sent to or received by them. In this example, the goal is to not display the Delivery Reports tab in ECP so it's not accessible by a user.
More info: Exchange blog