Although as the defender you should usually be pretty certain if ACMs are looming on the horizon...
Indeed, it's hard to make a case for not employing ACMs if you have them, but maybe that's just because I underestimate the brutality of the face-up cards - especially when that war criminal Jan Dodonna is lurking around.
There are some face-up cards in there that ended the game for me. ("Oh, you had an engineering command planned? Well, now it's a squadron command.")