In what scenario can a pilot use ballast?

Ballast is used to help adjust the center of gravity (CG) of the aircraft, especially when it is positioned too far forward, which can lead to control difficulties during flight. In situations where the CG is forward of the acceptable limits, it can negatively impact the aircraft's performance, making it harder to control or requiring greater control input for maneuvers. By adding ballast, the pilot can redistribute weight to bring the CG back into the safe operating range, thereby enhancing stability and control during flight.

While the other options might seem logical in certain contexts, they do not accurately represent the primary purpose of ballast. Increasing weight for landing or enhancing lift would not typically involve the use of ballast, and balancing uneven fuel consumption may involve other mechanisms like fuel transfer rather than added weight.