I use 3-needle bindoff frequently, but I always block the pieces first, then seaming the shoulders is last. As a matter of fact, on this cardigan I would block the Fronts, Back and Sleeves, then seam the shoulders, then pick up the stitches for the collar and buttonbands. Then, seam the sides and sleeves. Then, after the entire sweater is seamed, I'd lay wet cloths over top of the collar and buttonband ribbing to 'set them'.
I put the live stitches on the shoulders onto waste yarn during the blocking.
I block first because the pieces are flat, and still small enough to maneuver around on the blocking board.