This is one reason why I think that carb cycling is good. You see eating enough protein, many carbs and many fats is the diet that is supposed to increase your testosterone and build muscle (combined with enough sleep). But such a diet is only possible when bulking. When cutting you need to either lower carbs or fats. Lowering carbs will make your workout performance suffer and lowering fats will make your testosterone levels suffer (maybe). So here is where carb cycling comes into play, when cutting. The days when you exercise you should follow high carbs and low fats but at the rest days – high fats low carbs. In general carb cycling is not necessary, but maybe it will help keep testosterone levels high while cutting.