Unassign Purchasing Organization to Plant or Company Code

[Riyad_Abuzeid]

Hi all, 

As known, there are 3 types of POrg in SAP. 

1- Client level/Corporate-Wide/Centerlized POrg. Responsible to purchase for all company codes.

Assignment required: Assign POrg to all required plants under the different company codes. No CoCd assignment required in this type. 

2- Company Code Specific POrg. Responsible for buying material and service for all plants of a particular company code. 

Assignment required: Assing POrg to single CoCd + assign POrg to the required plants under this CoCd.

3- Plant-Specifc/Decentralized POrg. Responsible for buying materials and services for a single plant. 

Assignment required: Assign POrg to only single/one plant + assign POrg to CoCd of that plant.

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I wrote above forms of POrg to give you a picture of what I understood. 

My question is:

Is above relationships/assignments of the different types of POrg correct?
Also, for the client level/Centralized POrg assignment, I wrote the required assignment for this form is to assign POrg to all reuired plants. But what if I leave the existing POrg without assignment!!
I noticed that even though I leave the POrg without assignment, i can create PO. so,

Client level/Centralized  POrg assignment could be done by assigning POrg to all plants or leaving the POrg without assignment?
This is correct?
Sorry for typing this much of words. I hope somebody can assist me on this. Thank you