Dropship orders in Demand and Supply Planning

Summary:

Dropship Sales orders Collection in Supply Planning

Content (please ensure you mask any confidential information):

We have a requirement to collect Dropship Sales Orders in Demand and Supply Planning. I understand for Drop shipments to be collected only Item Org can be enabled as Dropship validation org and not any inventory organizations.

Having said this, please advise the Pros and Cons of having separate item org vs using Item master org.
When I enabled Item master org as Drop ship validation org and select the option to collect Drop shipment Demand and Supplies, the Supply Plan took 15+ hrs. to complete and not feasible. Without selecting this option plan completes in less than 30 min for Shipment orgs. Demand and Supply Plans are scheduled every day.