Think of it this way -- you are given your choice of two hammers, one steel and one aluminum. Now, the aluminum hammer will definitely be lighter to carry around all day long, and easier to swing, too; but if you plan on doing more hammering than toting, the steel one will outlast the aluminum one.
So, if you always want a hammer with you, but only plan on pounding an occasional nail, that aluminum hammer will last a long time and hammer quite a few nails along the way, and you'll barely know you're carrying it -- but the steel one will pound nails all day, every day and still be useable when you pass it on to your grandson.