Ankle dorsiflexion, the motion of moving your ankle in order to pull your toes up toward you, is essential for proper squatting and kneeling mechanics. Due to most shoes being made with an elevated heel, sitting many hours of the day, and not stretching/mobilizing to maintain proper dorsiflexion, people tend to lack the necessary motion.
In order to obtain a full depth squat, with the hips below the knees and torso upright, the lower leg needs to move forward slightly at the ankle. If the ankle does not have the motion to get there, the body must compensate to achieve the task at hand.
One common compensation is a forward trunk lean, placing stress on the low back. Add any sort of weight to that, whether it be with a barbell at the gym or lifting a box at home, you are placing your back at a high risk of injury. This method also places increased stress on the knees. It is not a matter of “if” you will experience pain or an injury, but “when” and “where” the injury will occur.
The other common compensation is taking the feet out wider, which if you are going to compensate, this is the safer compensation. This allows your torso to stay upright while allowing your lower legs to stay more vertical, rather than needing to lean forward on the ankles.
Check out this previous YFF video for a great ankle mobility drill.