Webform-CiviCRM and the "my billing address is the same" checkbox
This feature has not been implemented in Webform-CiviCRM. If you do see that box in a webform, it's a mistake (and the fix is to remove profiles from the contribution page you are using for the webform).

Implementation of this feature would require writing some javascript to fill those fields from available data, and some php code to store the data across potentially multiple pages. The best place to put it might be in wf_crm_webform_preprocess::addResources.

Note that if the user is logged-in then the billing fields will already be pre-filled.