The MDM repository is outdated and it is present to be complaint with previous versions.
Master data management (MDM) repository is used to create object by "top-down" scheme. The system automatically generates data on the structure of a created object and the user sets up the end object structure via interface in accordance with requirements. For example, when a "bottom-up" scheme is used to create a dictionary, it is required to create a table first (specify fields, indexes, adjust properties, determine keys and so on), and only after that the dictionary itself can be created (the attributes and structure determined, the units linked and so on).
Using an MDM repository, a dictionary can be created without creating a table. Basic dictionary parameters are already determined and it is required only to make corrections.
See also:
Creating Other Objects | IRdsDatabase | Working with MDM Dictionaries