The Kang Squat is an excellent exercise to add to your warm-up if you have squat session in store or if you are pulling from the floor.
If you have stiff hamstrings the exercise provides a great stretch, which improves the starting- and bottom position of the snatch and clean and especially improves any buttwink you might have when you squat deep. If you, like Micha Ostergaard in the video, are already really flexible then the Kang Squat can improve your understanding of how to find not an arch but a good old flat back and to then keep that tightness through the movement. Sometimes people do round their back not from a lack of flexibility but either from a lack of stretch or poor motor control.
A great way to warm up your front rack and bottom position before a heavy clean session.