Landry is one tweak away from jumping a HUGE triple jump. All she needs to learn is how to correctly use her back leg to forcefully prepare and execute a proper step phase. Too often athletes simply lift the leg upwards instead of swinging it for additional power and momentum. This drill forced her to swing it properly and drive her knee to maximize the movement's potential.
It also helps to slow things down so the arms are used correctly as well - which is a big deal in the triple jump! Without proper arm control athletes tend to become unbalanced and thus lose their posture. This results in jumps that are far shorter than their abilities.
Lastly, and possibly most importantly, it helps athletes to become more comfortable with the proper takeoff leg rotation. This is probably the least talked-about aspect of the triple jump. With a proper hop (takeoff leg) rotation step phases become much more likely to occur in a proper/explosive way.