You're talking about feed-days right? Where you eat complex as well as simple carbs to replenish glycogen stores so you have enough energy for your workouts? Well if you are staying totally away from simple carbs most of the time but still eating complex carbs, some people tend to still get low on glycogen so they need to "carb up" once or twice a week. Is this what you are talking about? Now if you do this be very careful, do not eat too many simple carbs at once. If you do, all the carbs (glucose) which are not used for energy, will quickly be stored as fat. This is the reason to not eat too many grams of simple carbs at once.