Fats are a concentrated form of energy which help maintain body temperature, and protect body tissues and organs. Fat calories in food are readily stored, while it takes energy to transform protein and carbohydrates to body fat. The only proven way to reduce body fat is to burn more calories than one consumes.
Most saturated fats tend to be solid at room temperature, with the exception of tropical oils.
Butter is high in saturated fat, while margarine tends to have more unsaturated fat.