From: US Midwest
If I am not mistaken, winning the Finland Expedition makes Finland lean Allies pretty strongly. This would mean that they would not join Axis automatically when Barbarossa begins, and that is a pretty big deal. And you get free units out of it to boot. So, even though the Soviets mobilization takes a hit, the Allies get enough out of it that, by itself, this is not game breaking.
Banning the French Communists makes the French last longer, which depending on your strategy, may or may not make sense. Again, not game breaking by itself.
But, when both options are taken, the combined effect is rather profound. Especially if you mix-in maybe a poor decision on the Molotov-Ribbentrop revision, then you have something that may be game breaking, but it is the players choice to do these things together. You have to keep track of your gambles, try not to arrange them so that the odds stack-up against you. If you do something to reduce Soviet mobilization, try to do something else to raise it.
A nasty gamble is to take full advantage of all the things that reduce Soviet mobilization, then rely on major-power diplomacy to bring it back up. Risky, but the results could be spectacular.
Lock up your wife and children now,
it's time to wield the blade...