Use of Inventory Org in Shared Service Procurement BU

Summary:

I am trying to perform a Proof of Concept on Shared Service Procurement where One Central Procurement BU serves 2 Requisition BUs in 2 different Ledgers.

For Example, Our Client has 2 Ledgers and 2 Business Units [Ledgers: IN1_P, IN2_P, Requisition BUs: IN101, IN201] and i would like to create a procurement BU IN300 which serves the Requisition BUs IN101 and IN102. As per the white paper it mentioned, right accounting is derived based on Inventory Orgs, I will have separate Invertory Orgs for IN101 and IN102. Now, the question i have is what should be the Inventory Org and what is the significance of inventory Org for the Procurement Business Unit IN300? Please clarify on this. Reason for considering the Shared Services is to SImplify