The voltage and current at the device terminals follow a load line, and the power dissipation inside the device is large compared with the power delivered to the load.
The "operating point" of the circuit in this configuration is generally designed to be in the "active region", approximately between middle of the load line and close to saturation point.
Care must also be taken to ensure that the rails remain straight, without resulting in dipped joints, which can cause wear on high speed and heavy axle load lines.
