Final answer:
To avoid inefficiency in air brake systems, it is important to bleed out the air in the brake lines due to the compressibility of air, which can result in a delay before the brakes are engaged fully.
Step-by-step explanation:
You should avoid compounding the air brakes because air is compressible, meaning it can decrease in volume under pressure and then return to its original volume when the pressure is released. In an air brake system, this compounding or compressibility can lead to inefficiency because when force is applied to the brakes, the air would first compress and warm before maximum braking force is achieved. It is crucial to bleed out the air in the brake lines to ensure the brakes work properly, allowing immediate transfer of force to the brake mechanism for prompt deceleration.