Triggerhappy said:
Pretty much, yeah. Only buld Flak when you've got nothing better to spend your IC on.
I disagree. When playing some countries, Germany for example, you need to put a good few provinces into upgrade mode anyway, in order to keep your resource consumption for CG under control. Some provinces have a use for AA, and those are good candidates. After all, building up IC is kind of a waste. You'll either end up conquering more IC than you need, or you won't have any use for IC because you'll be too busy learning to speak Russian. For Germany, good places for AA are the Ruhr provinces, Kiel (to protect your ships in port) and the provinces south and west of Berlin (to protect Berlin from being nuked). You cannot always count on your interceptors stopping ALL raiders, since they can only intercept one group at a time. The Americans love slipping in nukes this way.
Russia also has a use for some judicious AA building in certain spots, notably Vladivostok and along the Russo-German border. The border AA helps your ground troops shake off German tac bombers, and the Japanese love trying to bomb Vladivostok. By putting AA in these places you free up some of your fighters to make air superiority runs into enemy territory.