Load banks are used to test Generators or other electrical power supplies such as UPS systems.
Loadbanks are connected direct to the Generator and simulate electrical load that can be controlled using the load bank control system. Loadbank testing is vital to test your Generator to therefor prove your Generators capability to run your building load.
Alternatively loadbanks are used to add increase load for when a Diesel Generator has ran "Low Load" for an extended period of time. The consequences of low loading is the engine not reaching optimal operating temperatures therefor leaving unburnt fuel and carbon deposits within the engine and exhaust system.