At some point you may need that one more IPC to get 1 more VP, this often comes from China but not until round 4-7 or so. On turn #1 I ignore China for the most part, but do hit them in 1-2 places in overwhelming numbers so as to decrease my losses. It’s no good to trade 4 to kill 2 then lose the 2 left in a counter-attack of 2 INF and 1 FTR. Try not to even let the allies use their offense to attrit your Jap units.
As the game progresses you might see opportunaties to use overwhelming power to attrit the chinese forces, and here is the key, overwhelming power that isn’t being used or doesn’t hinder your ability to project power against the advancing US fleet. I love to keep 6 or so fighters and 2 bomers on Formosa. If the US moves up to within 1 space of the Caroline Islands where the combined Jap fleet sits then those air units fly out to attack and land on the CVs. The fighters on the CV attack then land back at Formosa. Otherwise they can still fly in 2 territories inland (3 with bomber) which exerts heavy offense over a wide swath of territory.
There is no sense going deep into China if it takes away from your offense against the incoming allied fleet again, unless you need that 1 more IPC to get that precious VP.
BB