It means you don't have to have a separate table to define a relationship between the object and the cr_item.
For a user, that might mean the user's file-storage root folder, and for a revision it could be a thumbnail image of that revision (which we do here).
This allows you to quickly get any items you need for an object in the context of a package, such as file-storage where you need to know which files to show for a specific user, or in a forum where you need to list available attachments.
-- NJL
