Save Layout allows you to save over a layout you have previously saved. It is commonly used when you have added or removed metrics, or re-sorted metrics in a layout and want to save without creating a new layout.
Note: When using this you will automatically save over whichever layout you currently have selected. The name of the layout that is currently selected will appear to the left of the Layout button on the screen.
Save Layout As
This button is used to create a new Layout. Once you click Save As you will be prompted to save the name of the layout (use a unique name). You will also have the option to make the layout Private or Public. If you select Private, you will be the only user that can see this layout. If you select Public, all users in your account will be able to see the layout.