1: You propably had to blow up something with it. Really, I don't remember that mission too well...
Wait. Was the last NOD mission not that one where you had to destroy three GDI bases? I can't remember a commando unit in it... :blink:
2: It's single use only. Sometimes you can cripple the enemy with it (Destroying the vehicle factory and construction yard), but if I'm right that's not the case in the campaign. Imho you should use it to injure the enemy defense as much as possible just before your assualt.
I always thought it quite useless compared to the ion cannon.