Saving the form vs Publishing the form

Based on my understanding, the notion of publishing is central to Form Builder/Form Runner.  A form becomes available by form users for data entry only after the form is being published.  I just want to understand the difference between these two actions in terms of persistence of the Form.  I noticed the REST calls during these two actions.

In case of saving the form the REST call looks like:
/crud/orbeon/builder/data/[FORM_ID]/data.xml

But in case of publishing the form the call looks like:
/fr/service/exist/crud/[APPLICATION NAME]/[FORM NAME]/form/form.xhtml

Also I think the data.xml and form.xhtml have same content.

So when a form user tried to enter data for a form, what is being verified to know if the form is already published or not.  Please clarify.

Thanks, Anjan