Squat variations

Due to inflexibility, injury or other problems, not everybody is able to do the back squat with correct form. Or you can throw in other exercises just for more variations in your training. Switching to a new exercise can get out you from boredom, or it can help you break through a plateau.
Every exercise trains your muscles and nervous system in a - more or less - different way.

Squat

Squat is the most important and most effective exercise for strenght building, therefore this is the most important exercise for vertical jump development. Due to hip and/or ankle immobility not everybody can make full squats with correct form. They have to choose one of the alternative exercises like half squat, front squat, etc..