Linked from
The 10 pages that link to Automatic generation control, each with the reason it gives.
Load balancingBroader topic: It continuously corrects imbalances after fast frequency response.
Economic dispatchRelated: It implements small, continuous output changes around dispatch targets.
Dispatchable generationRelated: It sends rapid setpoint changes to generators providing regulation.
Power system stabilityRelated: It helps restore frequency after generation-load imbalances.
Ancillary servicesBroader topic: It dispatches resources to provide automatic frequency regulation.