Well, a drafted army is not very good for interventionist police action around the world. First you have to train them A LOT (something that's not so difficult with volunteer army), then you have to equip them (which is expensive if you want to keep your technological advantage as big as it is right now), then you have to maintain morale among the troops ("hey wtf why are we here in butt****istan dying for no obvious reasons") as well as home front ("MAH BABY BOYH JUST GOT HIM KILLED IN BUTT****ISTAN OMG i say we hang them by their necks and kill em till dey die you leaders"), you have to be able to somehow explain the inevitable casualties to populace and so on.
A conscript army is pretty powerful political leverage which hampers interventionism, unless you're a 3rd world ****house or a dictatorial nuclear power (think Russia!).