Can I sort, label, or pack goods while the packers are there?

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If you do, that will delay the packers/movers and greatly reduce the efficiency of their packing and loading.

Do I have to be home when the packers are there?
Can I instruct the movers a) what to pack first b) what to load first c) how to maximize the efficiency of space use in the shipment d) how to load goods one inside the other?