Every circuit are usually more inductive than capacitive.it means that the current lags by voltage at small angle.hence we have to compensate this situation so we use Capacitor then this lag is compensate by leading current angle.total power =VI cos(phase angle)

Phase angle becomes low and the value of cos(phase angle) is increase and hence power also max.

Phase angle becomes low and the value of cos(phase angle) is increase and hence power also max.