Aerobic exercise is helpful to improve circulation and to burn calories and, if done long enough, to also help burn fat stores. When you do resistance training, the goal is to strengthen muscles and hopefully build/maintain muscle mass.
Muscle weighs more than fat tissue, so many times people do not see a weight loss but may in fact see a slight weight gain as they increase their muscle mass. The benefit of increasing your muscle mass is that it can increase your metabolic rate, which will utilize more calories per day. If you kept your calorie intake the same each day, you should eventually see a weight loss.
Many athletes change their workout routines to include not only a variety of muscles areas, but they also alternate between aerobic style exercise and resistance training to allow the benefit of both types of exercise. By alternating the exercise routines, it also allows those worked muscles to rest /heal between workouts.