Muscle is living tissue, unlike fat which is just stored energy. Just like any other living thing muscle requires calories to survive. Muscle uses calories just to stay on your body. So the more muscle you have the more calories you will use to keep it there.
When people want to lose weight they automatically turn to cardio exercise. This will help you lose weight but most people are not aware of the fact that much of the weight that they will lose will be muscle and not just fat. This is a mistake because the smaller the muscles, the fewer calories they will burn, and because of this weight loss results will begin to slow down and become more and more difficult. You will have to do more and more cardio to keep the results coming. This will leave you a body with little muscle tone which is not always attractive.
Many years ago weight training was considered to be a method of training used only by strongmen and bodybuilders. Many people would look at the large muscular bodies of these athletes and find them freakish and unattractive. Many people looked down on this type of training because they felt that having lots of muscle slowed you down, made you muscle bound, and made you look like some sort of freak.