The Pull-to-Knee is an Olympic weightlifting derivative exercise. What does this mean? Simply, it is a more simplified version of a Olympic weightlifting exercise, or, as in this case, a part of a weightlifting exercise (by the way, the full weightlifting exercises are the Clean and Jerk and the Snatch).
The value of using weightlifting derivates is that the exercises are much simpler to learn and do not require either significant practice time or specific body anatomy to perform. In my experience, most athletes (myself included) do not have the requisite body anatomy, such as hip joint architecture, wrist flexibility/joint architecture, or thoracic spine (i.e. mid-back) mobility to successfully complete the full versions of the Clean and Jerk and the Snatch. However, as suggested by research, nearly all, if not all, of the benefits of the Olympic lifts for athletes are attainable with the Olympic lifting derivatives.
The ankle, knee, and hip angles in the Pull-to-Knee are similar to those in the first few steps of an acceleration run, thus making this lift applicable to nearly every athlete. In addition, because of the more horizontal angle of the torso in the Pull-to-Knee, it can help build lower back strength. But, this can also pose a risk to athletes if they try to use too high of a weight.