I have now discovered a use for your mark as fulfilled on a sale where there are drop ship items.
To supercharge this it would be useful if:
a) In the Fulfilled view you have a status field of Invoiced/Not Invoiced. This in theory allows us to control when a drop ship gets invoice. However, you can only sort by one field at a time and cannot filter a secondary field. Ideally we would like to sort by date required and filter/sort by invoice status as a secondary element.
b) Add the drop ship PO number to your search index for sales. That allows us to skip the step of going to the PO and then linking to the sales order from there. Instead we can go direct to the sales view, search for the PO and mark as fulfilled.