An impulse to imagine fighting, even when you are not, is an opportunity to rehearse the techniques and learn from mistakes.

It is my observation that people seldom have very realistic ideas about what's involved in a fight unless they have some training or hands-on experience. Scenarios like that don't really have a lot of bearing on practical technique, so I'd be rather surprised if this emotional experience were best explained by there being a brain-module that rehearses hypothetical fights instinctively to increase people's odds. It seems like a logical implication would be that people with this trait fare better in physical competition, and if it's a standard trait of humans, then why are we so abysmal at instinctive combat?