The upper back and lats essentially perform in an isometric fashion during the conventional deadlift. The problem is, the start of the movement is initiated by a push off the floor using a degree of knee extension, then the movement is finished through hip extension.

With partial deadlifts (from the rack or off blocks), you can eliminate the push off the floor and instead focus largely on the upper back and lats, making them do most of the work.

Why Bands?

With the addition of bands, you'll make the lockout even more difficult and force the upper back and lats to work even harder to "hold position" and perform isometrically. Even in the top position the entire back will still be under a tremendous amount of tension just to hold the weight in place.