Here's a real-world situation where an order with no effect is useful.
Italy and Austria are allied against France. France is about to descend on them with an armada of fleets, so Italy and Austria need to build two new fleets immediately. It is a Fall turn, and neither Austria nor Italy will get any builds as it currently stands (Italy owns Tunis). How can Italy and Austria be assured of building one fleet each?
Austria: Army Tyrolia -> Venice.
Austria: Fleet Adriatic Sea SUPPORT Army Tyrolia -> Venice.
Italy: Army Rome -> Naples.
Italy : Army Apulia SUPPORT Army Rome -> Naples.
Italy: Army Venice ???. (*dislodged*)
Italy can clearly gain a new fleet in Rome by recapturing Naples. Austria could also build in Trieste if he gained another supply center, so Italy must give him Venice. But if Italy gives up Venice, he won't get a build unless the army in Venice is also destroyed. Therefore the task at hand is to assure that Venice is destroyed no matter what France does.
The problem is that if Venice simply holds, then Piedmont might support Venice to hold and the plan would fail. So Venice must move somewhere -- anywhere -- to prevent France from supporting the unit to hold. But where can Venice safely move without potentially interfering with the plan?
