Did you ever notice that S/O Packing List Printing can be accessed even if ""Shipping"" is not enabled? I know it does this on 4.40 and 4.30. (On 4.05 it says it's not enabled.)
It kinda gives the false sense that it can be used without enabling ""Shipping"" but it's still my understanding that it can only be used for Shipments/Invoices that were generated via Shipping Data Entry.