Sugar is a carbohydrate and has a significant caloric value. While not a "nutrient" in the normal sense, of course calories are important to sustaining life. Most of us here are trying to limit our calorie intake so we think of sugar as "junk" but in the big picture it is pretty important to human nutrition. Complex carbohydrates are digested into simpler sugars and it is the sugars that the body gets its energy from.
The reason FitDay doesn't have a separate column for sugar is that all sugars are lumped into the carbohydrate catagory. It would be nice if FitDay could separate out the sources of carbohydrates (complex, starches, simple - i.e. sugars) beyond just fiber the way it does for fats, but at the moment it doesn't. But rest assured that the sugar contents in the foods you are putting into your created foods are beng counted.