SharePoint Designer is a single tool that helps you do so much more with the SharePoint, with little or no coding.
In the Share point designer 2010 there have been some enhancements and as an Administrator its important to understand these enhancements.
Features such as Contributor settings, Database Interface Wizards, Site Publish, Site Backup and Restore are no longer available in the Designer 2010.
Additionally SharePoint designer offers new capabilities to create web part pages, master pages, lists and workflows, setting permissions for individual users; and saving and deleting site templates.
Also you can extend share-point 2010 ribbon using standard Development APIs to fulfill application & corporate requirements using SharePoint designer 2010 you can customize both Ribbon and drop down lists to display site lists, available webparts, workflows, or other information as needed.
refer the link http://technet.microsoft.com/en-us/library/cc179083.aspx to get more information on this part.