Soya flour is extremely rich in protein, so it can be added to any food to enhance its nutritional content. It is often used in commercial products such as crisps and sausages. For the home cook, it is valuable for baking, making flat-breads, and thickening sauces. It is often combined with wheat or other grain flours before use.
Details about soya flour taken from here but there is also more information about soy flour (soybean) at Wikipedia here which you may like to read.