Another classic gym theory was proven by this study – wide stance squats cause more glute activation while narrow stance squats cause more inner quad activation. Use both squat stances in your training to maximize leg development and squat strength.
Reference: Paoli, A., Marcolin, G., & Petrone, N. (2009). The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. The Journal of Strength & Conditioning Research, 23(1), 246-250.