My observation has been that many fitness and personal trainers believe more in going to the extremes i.e. 'lift all the way', 'squat all the way down' or 'lift the heaviest and as maby reps as u can'.

On the other hand, as a physiotherapist, and considering the bio-mechanics of the knee joint, deep squats strain the knee remarkably, as more reaction forces are directed into the patellofemoral joint as you go lower with the squat. Even higher strain will be directed into the knee joint as add/carry weights. As such I would recommend only up to 90 degrees knee flexion.