is MDM customer master strategy

What is MDM customer master strategy implemented in case of CRM, R/3 and other systems in CMDM scenerio.

The Customers are created centrally in MDM and sent to all the systems?

or

The Customers are created as Business Partners in CRM first and then they come to MDM and gets created as Customer.

or

something else ?

What and how you done in case of your implementation experiences ?

Sandesh