It may help with an all out KJF plan if Russia decides to ignore the German advance and become a thorn in Japan’s side.
It may allow for more US resources to be directed at Europe, but they may be too little too late if Moscow were to fall easily and/or earlier than it should to the Germans.
I’ve played it out a few times, with significant Russian intervention in China, but Russia gets zero economic benefit and places a lot of resources in China that have little impact mid-late game for a crippled or defeated Moscow.
As the highest quality play by Japan is minor IC on the mainland, Japan can send 3 Mech with aircraft flown over them to clear out small infringements of the Russians in China.
IF I were to create problems for Japan, on R1 I would:
Buy 1 Arm, 2 Mech, place them in Stalingrad.
Move 1 Arm, 1 Mech from Moscow to Stalingrad.
Keep the 1 Arm, 1 Mech that start in Stalingrad there.
Fly your 2 Ftr and 1 Tac to Stalingrad.
R2 move into China (Sikang)
UK2 DOW on Japan (if not already at war) move all ground units into Yunnan, which hopefully is a reinforcement, but it may be a liberation depending on how China does there.
R3, move those units from Sikang into Yunnan, reinforcing the Brits and probably halting a Japanese takeover of the Burma road there.
I’m not suggesting this strategy. But it WOULD create problems for a Japan player that does not build IC on the mainland. Additionally, if UK has to DOW on Japan, this places the US out of the war for a while, which further hurts Moscow in the long run.
Of course, those fast moving units in Stalingrad can:
Be redirected to NW Persia on R2 if at war, and they are more than enough to claim Iraq and get some additional income for Moscow - so there IS flexibility.
If Moscow is still waiting for war, those units can all move directly to Bryansk on R2 and be in position for a R3 Strafe anywhere in Russia that Germany ends up on G3.
Personally I’d suggest one of the two options directly above before intervening in China. There is little economic benefit unless you are in a KJF Allied strategy where bogging the Japanese down in China creates immense economic problems. In particular I wouldn’t want Russia playing a defensive strategy in China throwing its units to the wind. I’d rather be able to blitz across Northern China, far away from any Japanese IC and/or reinforcements.