If you edit an existing Document Type in DBXL you’ll see a button labeled Save As in the header. This is an easy way to create a duplicate of your configuration, but under a different name.

Why is this useful? Here are two possible scenarios:

• Database mapping: Because this action copies the Database mappings, this is useful if you wish to avoid recreating a large mapping to SQL. This also allows you to create the same mapping but to a new database or SQL instance, by replacing the Connection String.
• Development and Testing: Save As allows you to create a test DocType. You can edit the InfoPath form, create test documents, edit the SharePoint or Database mappings, or alter Permissions. Once you have tested, you can edit your original DocType to apply whatever changes you wish to implement. This way, you avoided altering your main Document Type (which might be in use by users in a Production environment). 

These are but two scenarios where the Save As button might prove useful.