A foot spacing greater than shoulder width puts a little more emphasis on the adductor magnus. If the feet are wide apart, it is called a sumo squat.
Placing the feet at 11:05 a.m. instead of 10:10 a.m. puts a little more emphasis on the vastus lateralis of the quadriceps, but it is more likely to round the back for the same range of motion.
This weightlifting exercise requires a full movement, high bar (on the trapezius, just below the neck). Due to the center of gravity, the thigh flexion occurs mechanically with the back more vertical, which emphasizes the work of the quadriceps and decreases that of the erector spine. The full flexion position, facilitated by the use of specific heel shoes, accentuates the work of the gluteus maximus. Keep the thighs under tension even at the bottom of the movement and don’t bounce off your calves.
This powerlifting exercise is just below the Low Barre parallel (on the middle trapezius and posterior deltoids). Due to the center of gravity, the thigh flexion is initiated by the hips moving backwards and done mechanically with the back leaning forward enough, which emphasizes the work of the hamstrings and spinal erectors.
High bar, using flats and placing a wedge under the heels, you find yourself in a bit of the same setup as a weightlifter squat.
The partial or quarter squat is performed with a movement varying in amplitude from flexing a few degrees to parallel. It is used in physical preparation for athletics, by strong men, or occasionally by power athletes.
The squat can be performed on a Smith machine, with the feet very far forward so as not to put too much strain on the knee joint. Dorian Yates found the Smith machine squat to work better than the barbell squat for strengthening his thighs. In physical preparation or power training, of course, the Smith machine squat is of no use.