In the past, if you updated a compatible unit (CU) within the library, you'd also have to update each and every favorite that contained a copy of that CU. CU referencing eliminates this need.
With CU referencing, favorites no longer contain copies of CUs. Rather they contain a reference or a pointer to the original CU in the CU library. If you update a CU in the library, that change will be reflected in any favorites that reference the CU. This functionality is integrated into Designer and requires no configuration.