Vehicle fabrication.
The Garage and its kit assembly line allows the requisition of Ghost, Wraith, and Locust vehicles and unlocks their upgrade options. The Foundry is critical to the creation of combat and support vehicles that the Outpost overseer can use to better exploit his surroundings and eliminate UNSC opposition to the Banished's plans.
The Banished were raiders and reavers for years. until the breaking of the Covenant allowed them to consolidate and build themselves into a true power in their own right. Atriox's brilliant strategies are unconventional when necessary and imitative when efficient—for he will adopt whatever techniques and technologies he has to in order to guarantee victory. His use of Engineers and compact assembly vats in forward bases would have been considered unorthodox - even heretical - under the Covenant's traditional war creed, but those days are past.