When an AI controlled commander's gun on a tank runs out of ammo, it causes the AI controlled coaxial gun to have a magazine reload cooldown after every few rounds fired rather than just when it's supposed to load the next mag. So until you refill the commander's gun's ammo (or get the AI out of the com seat), this essentially removes the coaxial from being properly used by the AI since it turns it into a slow, one-three shot weapon. Vehicles with low amounts of ammo for their commander's gun (such as the T-100) suffer particularly from this as they're far more likely to run out of com gun ammo while in combat (thus also removing their other primary anti-infantry weapon).