A Brit IC in South Africa coupled with a strong US Pacific presence can make life a merry hell for Japan. Add to her difficulty by sending a few Russian infantry into China and suddenly the ‘unstoppable’ Japan has a whole lot of problems to deal with. In turn, this relieves pressure on the British Empire and on Russia since Japan isnt gobbling up the backfield and threatening the 2-IPC territories east of Moscow.
Personally I think a SA IC even if ALL it does is help save Africa is worth it. And 2 tanks per round can really put the hurt on Italy in Africa, again saving Brit IPCs each turn. I’ve found that that factory eventually pays its own IPC cost off in saved territory in a few turns and thats not counting the hurt that inflicts on Italy or the potential to irritate Japan.
A Brit factory in India is a target for Japan IMO and most J1 moves I’ve seen played leave enough firepower to bear on India to take it (a costly attack, mind you) if the Brits build the IC. Australia is the same way - there is just no way to guarantee holding it long enough use it. The only safe spot is SA and I think its actually more useful than Australia would be since it helps with Africa as well as providing potential Pacific pressure.
I suppose if Russia wants to commit a LOT of infantry to defending India, the Brits might be able to get away with it, but it still a risky area IMO. Japan can bring an awful lot of firepower to bear quickly if its ever weakly guarded and that really cuts down on its utility IMO. And Russia without 4-5 extra infantry in the south is gonna feel mighty fragile for a while. Granted it will likely head off a lot of later Japanese pressure as well, but in the short term you might lose a lot more if Germany/Italy breaks in down south.