I’m going to disagree with the statement that “…pretty much everyone turns their feet out slightly”. I tend to vary my foot placement, and, I know of others that do also. This includes ‘neutral’ (toes forward) placement.
There are reasons to squat with different foot placements. A 2013 study, Effects of Foot Position during Squatting on the Quadriceps Femoris: An Electromyographic Study showed that foot placement did affect activation of specific muscle groups. Four foot placements were studied and the effects of each were recorded using Electromyography. The study showed that foot placement activated those muscle groups differently based on foot placement.
In addition, in SQUATTING KINEMATICS AND KINETICS AND THEIR APPLICATION TO EXERCISE PERFORMANCE, looked to:
“…examine kinematics and kinetics of the dynamic squat with respect to
the ankle, knee, hip and spinal joints and, second, to provide
recommendations based on these biomechanical factors for optimizing
In particular, in regards to foot placement, the article may provide some insight into the advice you were given:
“This suggests that a narrow stance may be preferable over wide stance
if the goal is to minimize compressive forces at the knee. On the
other hand, a narrow stance squat resulted in approximately 4 to 6 cm
greater forward knee translation and thus greater shear as compared
with a moderate or wide stance. Therefore, a wider stance might be
preferable for those seeking to minimize shear at the knees (18).”
The article then states:
“Several studies reveal that varying squat stance alters muscular
recruitment patterns. Escamilla et al. (18) found activity of the
gastrocnemius was 21% greater in a narrow versus a wide stance. McCaw
and Melrose (45) reported a wide stance significantly increased
activity of the GM and adductor longus, with greatest activity seen at
140% shoulder width. Ninos et al., Paoli et al., and Escamilla et al.
(20,50,53) also reported increased muscular torque of the hip
extensors and adductors in wider stance squats. Stance width has not
been shown to alter muscular activity in the quadriceps and
hamstrings, however (20,42).”
Given the above comments, I tend to vary my foot placement on leg movements. This includes squats, leg press, and leg extensions. I find that the variation allows me to optimize my leg training.