AI behavior in scenario editor

[terminator]

Hello,
In the scenario editor, you can choose the AI behavior of a unit.
There is Hold position active or passive: "Passive units will never move, but active units will move if there is a favorable tactical possibility (capture a flag, score a kill etc.)" .
That's right. Passive units will never move, but the problem is that passive units will never fire ! For example, an Anti-air passive unit will never fire against an ennemy air unit. Which is the utility of passive units ?
Thanks