We needed to do some custom modifications to data before it would be sent to Salesforce, so Matt created a patch to the salesforce module to provide hooks for modifying data that would run before the data was sent to Salesforce. This got the ball rolling on this idea and this functionality was added to the module.
This patch allows node relationships in Drupal to be synced up with object relationships in Salesforce using node and user references.
For example if there is a 'case' content type in Drupal, then you can add a user reference to it. When sending a case node to Salesforce, you can create a new Case object and link it to the user's Salesforce Contact.