FIghters can be so unreliable, due to bugs or wacky AI, that in general Hydran players will only launch fighters when they can be used for maximum effect. Sort of the exclamation point. Also the "Fleet in being" concept applies. I've gone entire battles where I didn't launch them - but where the enemy had to be prepared if I did. An illustration:
Harrass - exposes fighters to enemy fire, fighters may get too close anyway despite orders, missile armed fighters won't get close enough to trigger the missile launch routine frequently. Also totally useless in a multi ship enviroment, as they only maintain harrass range to the target ship and totally ignore others.
Attack - self evident
Defend me - even when working this command is very problematic. First, when set to defend, frequently when set, the fighters will move beyond a range that they will engage missiles or other incoming similar threats from your ship, making them unreliable for defense in this area. Second is that a acute enemy player will simply fire missiles at the fighters instead of your ship. Since the fighters are close to the ship, it is difficult to determine who is being shot at, and therefore problems can result due to this. Third is the fact that since fighters (as with all AI) have no concept of the idea of effective range, they will frequently fire their own weapons at ship targets and then be unable to screen your ship from threats. Fourth is the fact that if the enemy ship has a angle of attack (or better term, angle on the bow) of 0 degrees or thereabouts (IE pointing you) the fighters will switch their own orders to attack and then move to attack the target. This wonderful behavior is not a bug, but actually a "feature" based on a design decision. This will also happen if you move too close to the enemy ship, even if they are pointing away from you.
Basically fixing the defend me problem enables the return of the controlled fighter hellbore saberdance, a lost tactic in recent days. Breaking the fusion fighters in return though isn't exactly what we had in mind in return though.