Products.SimpleReference is an addon for Products.RichDocument to enable Image/File referencing. Image/File referencing gives you the ability to leave Image/File data at one defined place in your Plone site and therefore you prevent having duplicate data for each RichDocument.

SimpleReference adds two new types "ImageReference" and "FileReference" and overrides the widget templates of Products.SimpleAttachment to add these References via kss enabled viewlet.

Overriding SA templates is done because you are now able to sort ImageAttachments and ImageReferences (or FileAttachments, FileReferences) in one place.