As of now, duplicating a label sends it to the payment page which does not allow you to edit the order.
Usually the duplicate is not the exact same as the old order. So it's important to be able to edit the order slightly. We usually just need to edit quantities.
This is important for me to be able to manage these special orders quickly and effectively rather than telling my shipper "Hey ship John Doe 2x widgets". Instead I could just easily create a duplicate shipment, edit it if needed, and send it to the orders page for processing. Then it's a no brainer for my shipper, just like processing a regular order.
Plus this way customers don't get a tracking email from a duplicate order with the incorrect products or quantities.