This circuit is good for testing a power circuit with. It allows one to draw a specific current from it. It acts as a current limiter. The resistor towards the ground is to linearize the temperature dependency of the darlington beta value. Otherwise the current will rise as the temperature rises in a runaway effect until burnout.
If this circuit can be actively controlled by a microcontroller, then this resistor can be much lower, but can never be removed.
With current settings the load is sinking about 600W of power. About 2W is burned in the resistor.
