A Leaner Body. Effectively stimilating muscular development means improved body composition (body fat vs. muscle). More muscle means burning more calories at rest, making weight management much easier. Not only that, muscle gives us shape, as fat is shapeless. Changing your shape through fat-loss alone is very difficult and usually leads to a loss of muscle as well, leading to a "skinny-fat" look.
Stronger Bones. Just like muscles, resistance training applies a productive stress to skeletal tissues stimulating them to grow stronger. Particularly as we age, we need productive stress to slow or halt the loss of bone density. It could be the difference between getting a bruise and breaking a bone in a typical slip and fall on the ice.
Greater Strength and Endurance. More efficient muscles mean less effort in all things physical, which means you can do it for longer. Imagine never straining yourself in your normal daily activities. Having extra strength is like having turbos on your car. Do you really need it? Maybe not, but it sure is nice.
Improved Libido. Two reasons: First, simply feeling better about yourself makes it easier to enjoy yourself. Second, as you become healthier and stronger, things just work better... Eat your heart out, little blue pill!
Character Development. Training is hard. It requires the development and direction of your will. That changes you. After all, if it were easy, everyone would do it and everyone would be super-fit. We admire beauty and fitness because it is elusive. The effort of changing yourself physically provides lessons that are transferrable to other facets of your life. Training makes the whole person stronger.