Ghr is incorrect.� � Germany and Italy are not diplomatically tied like Anzac/uk and Germany is free to reinforce any Italian territory regardless of who originally controlled it, just like any other friendly territory.
Great, it’s a good option to have. If Italy can opens Eastern Poland and Baltic States on I3, I don’t see why I would declare war on the Soviet Union and lose 5 IPC in the process (the Russian fleet is stuck, the Vyborg / Karelia route is subject to counter attack), there would probably be no sizeable territorial gains to obtain anyway.
the russians can still counterattack, the russians can declare war on germany on the next ussr turn, the only advantage you do get as germany is that you get the NO, BUT you lose the ability to attack russian troops and landareas, so not always a good choise
Always good to have the option to do it though…