If true on a non-versionable element, you can only edit the attribute when you first create the element and before the element is saved to the database. You will not be able to edit the attribute from the DB Properties dialog.

If true on a versionable element, you can only edit the attribute when you create the first version of the element. The attribute will not be editable when someone creates new versions of that element.

If you add the <ProtectUnlessNew> tag to a name attribute, you can turn off the ability to rename models, drawings, etc.

This example shows a valid configuration for the tag: