This would let you import other order fields that Linnworks does not have.
What I would use this for is for cost checking when doing drop shipping. Suppose I import an order, and I charged 10 for the item and 5 for shipping. I sent the order to a supplier that will ship the order for me. He charged me 7 for the item, and 6 for shipping, and also added on a drop-ship fee of 1. If I had extended order fields, I can then set up three new order fields - "Real Cost" "Actual Shipping" "Other Fees". So I would import these purchase order values back into all my orders. Then I would create a query that will show me that after market commissions, adjusted shipping costs etc, if I lost money or gained. Another query could tell me that my estimated shipping and actual shipping don't match, neither does my calculated cost of real cost (sort of like reconciling purchase orders)