Using a wall during squats provides feedback to maintain an upright spine and develop mobility for a deep squat.

“if you want to develop here's a great way to develop flexibility for this type of rock bottom squat if you're not there yet uh initially even without resistance assume your normal squat stands and I'm talking about a narrower stands you know shoulder wi or somewhere there and approach the wall face the wall put your arms out and start squatting and you will find the wall is going to teach you so it is the feedback from the wall if you start doing something funny with your spine you're going to hit your head on the wall and fall back so it's it provides terrific feedback”