This is where the roughly cut wood supplied by the peon laborers is made usable by skilled workers for buildings, spears, and catapults. If other Orcs require specific woods for their sites, only your Lumber Mill will have the necessary workers to complete the task. When funds are directed to the craftsmen of the Mill, they can increase the quality of your spears, making them bite even deeper into the hide of the Human scum.[1]
Lumber Mills are used to upgrade the attack of your Spearmen. Furthermore, the construction of advanced structures is only available once a Lumber Mill is up and running.