This is considered to be a good mass-builder for the upper back and this video illustrates well how the muscles are engaged by the movement.
You can vary the grip width and angle of the back to suit. I prefer to have my back as close to horizontal as possible. I believe that the wider the grip, the less the biceps are engaged and therefore the more you isolate the lats.
I like this guy's videos. He just gets on with it. The only thing I would say is that he appears not to pull the dumbbell right into the base of his ribcage, which I find gives me a better squeeze.