Yes you are right, nutriton and being in a calorie deficite is essential to weight loss. But walking can be supportive just for the aid of psycological and hormonal benefits of it and not just the physiological. Movement is not just about burning calories, there are manay benefits to walking, reducing stress. Hormone balance is key to keeping your hunger and cravings in check. Which I believe is a key part and often an overlooked benefit of walking.