RE: What is the significance of reference field in a ...
Based on the value selected in a particular field if you want to pop-up DFF segments then reference field will be used.
eg:you have a field called Item. if you choose Computer as an Item then in DFF segments you want to show Computer Brand name Size. If you choose TV as an item then in DFF you may want to show TV name TV Color TV Inches etc
in reference field we enter :Item as Reference then in context values we enter the Item Values and then respective Segment names.