Sure. Sugar is a source of energy. Too much sugar or energy gets stored for a later time as fat. It doesn't have to be broke pen down so it is available immediately for use, so any extra is put right to fat. Sugar is not necessarily bad just getting to much to quickly is bad. We do better if our bodies have to work some to break compounds down to use them, instead of storing the energy right as fat.
No. Refined Sugar is source of calories, but is not essential for health. Complex carbohydrates are a better option than refine sugar. Having said that use of sugar in moderation is not likely to harm. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco or alcohol in any form. Practice safe sex.