The demesne lands were typically worked by the lord's own serfs or peasants, who were required to provide labor services in exchange for their land and protection. The lord would also often rent out some of his land to tenants, who paid rent in the form of cash, crops, or labor. The income from these rents was an important source of revenue for the lord and helped to support his household and retinue.
The amount of land that a lord kept for himself also depended on the political and economic conditions of the time. In times of war or unrest, lords were more likely to keep a larger portion of the land for themselves in order to ensure their own security and self-sufficiency. In times of peace and prosperity, lords might be more willing to rent out their land to tenants and focus on other activities, such as trade or warfare.
Overall, the amount of land that a lord kept for himself was an important factor in determining his wealth, power, and status within the medieval social hierarchy.