The purpose of this typer of exercise is to develop the oxidative capacity of the slow twitch fiber. By doing this you improve the ability of relaxation (high concentration of mitochondria) and for athletes the more then can use slow twitch in competition the less cost on the court of field (because they are purely oxidative). By increasing the cross section by 20% this will equal a 20% increase of speed at anaerobic threshold.
Except what it’s really doing is increasing the oxidative potential of intermediate fast twitch muscle fiber, which can adapt to become either more white (power oriented), or red (endurance oriented). Slow twitch are already oxidative and don’t hypertrophy to much extent at all. Increased mitochondria and glycogen storage capacity will favor better conditioniong though.