It's an exercise bodybuilders have been doing for decades. You've seen pictures of Arnie doing them. They've been credited for training the lats, pecs, serratus, and expanding your ribcage. Talk about bang for your buck!
While it's a great lift that targets a lot of muscles all at once, it does have one drawback. At the bottom of the lift the long lever arm means that huge degrees of tension are placed upon the lats and upper pecs. As you lift, however, this drops off significantly, making the top half of the lift (when the dumbbell is over your face) largely redundant from a muscle-building perspective.
The simple addition of a band anchored behind you fixes this issue.
When you do them like this, the band keeps adding tension throughout the range while the resistance from gravity diminishes as the lever arm shortens. All told, this causes your muscles to have to work harder for longer. That combo adds up to more growth.