Dynamics AX allows you to specify warehouses that are designated to refill other warehouses. This feature is really useful because it will make MRP top up the stock within the child warehouses through transfers rather than a purchase order, and then plan to purchase more product at the refilling warehouse to cover the demand. There is also no limit to the number of levels that you can have, so smaller retail locations can be refilled from area distribution centers, which could be replenished from a central production of receiving center.
This makes your purchasing a lot more centralized and stops you from nickel and diming your suppliers with small orders from each location.