The four specific areas that we want to mobilize in the Olympic lifts are:
Ankle
Hip
Thoracic spine
Shoulder external rotation
A lifter that doesn't spend time mobilizing these areas could have problems executing the lifts with any semblance of good technique. A lack of mobility in these areas can lead to compensatory patterns that could cause injury.
With the squat, you want to break from the knees and hips at the same time. This plyo drill can teach the correct movement pattern and fix bad patterns.