The shield generator acts as a command post for the Rebels on Hoth: Echo Base. However, if it is taken out, it ceases to spawn troops. Therefore, when playing as the Empire, it is best to destroy the Shield Generator as soon as possible to terminate the flow of Rebel troops that can easily take the 'Bunker' or command post 2.
The most straight-forward strategy for doing this would be using AT-ATs; because the bunker is opposite of the hangar, this can be dangerous and you could risk the snowspeeders destroying your AT-AT. Shock Troopers are most suited to the task of taking out the snowspeeders while your AT-ATs destroy the bunker.