Hi-
Save and submit are different operations.
Save asks the user to provide a name, and subsequent saves are done under that same filename.
Submit uses the form's submit data connection, or rules, or code, to submit the form.
So the question you'll ask yourself, as a designer, is whether you want users to click Save and then save the xml file with any name of their choosing, or whether you want to use a submit operation which controls the operation more carefully.