The Indonesian in me is cringing at how much ammo (read: money) is being wasted, while the soldier in me is crying '**** YEAH'
when you consider that the ammo in these guns is far cheaper than air to ground missiles, it seems lest wasteful. so in an air to ground or air to air role, its well worth having one.
the low caliber gatling guns used in choppers and on humvees has its role set as a fear inducer. the second you see that gatling gun roar to life and open up, you jump into your foxehole and pull your helmet down over your eyes. now i admit that when on the ground, the oppritunity for gross overusage of ammo is

greater. rather than a pilot who has a half a second window to pull his trigger, you have some gung ho soldier wio is abit trigger happy and has orders to lay down suppression fire, that ammo is gonna go quick.
as a suppression weapon is where that fear comes in to play, your job is not to hit the enemy, but to get him down on the ground while you either advance or retreat. if you should happen to hit the enemy, which is much more likely with a gatling, so much the better. you wont see gatlings issued to individual soldiers as standard issue any time soon.