I believe that finding the balance of drones would be putting a limit on how many drones a country can use at one time. I'm not sure on the other 2 questions.
It made settlement and transportation faster.
I believe the answer is: It caused the Roman empire to have a small and weak army.
By enforcing conscription, the majority of Roman soldiers were brought out to aid in the conquest to expand the Roman empire. When this happen, the defense for within the Capital become extremely weak and fragile. This make it easier for the invaders to attack and destroy the capital.
