Actually, there may be no advantage to fully automatic. I understand that when there was trouble years ago in Kenya (Mau-Mau), the Brits had trouble with an arms/ammo embargo and their soldiers were restricted to semiautomatic operation, to conserve ammo. They supposedly got better results than normal because they were aiming instead of just ‘spraying’. The combat kill rate in the US Army is amazingly low on a per-round basis.
Suppressive fire is a critical element of effective maneuver. While killing the enemy is certainly a desireable outcome, keeping his head down so he can't kill you has a quality all its own.