Osteoporosis is a major concern for women over forty. Osteoporosis is a condition in which bone tissue is reduced in amount, increasing the likelihood of of a fracture. Some studies report bone loss at the rate of one percent for each year after age 35. Resistance training has been proven to significantly strengthen bone due to the effects of Wolf's Law, meaning that bones increase in density as a result of the demands weight bearing exercises place on them. As far as weight-loss is concerned, weight training can help you there as well.
Muscle is metabolically active tissue which means it's like a furnace.
Muscle burns calories around the clock, even while you sleep, by increasing your metabolism. In fact, for every pound of muscle you add, your body burns an additional 50-100 calories daily. This helps the long term weight-loss goal of any program. This is mostly due to the natural decreases in muscle tissue that come with age. Muscle loss can be reversed with exercise of course.