The extra thread for diamond baffles vs horizontal is so minimal I doubt a postal scale would pick it up. Down will not shift as much with diamond baffles. Some people want to shift the down (for example shake more to the front of the coat). Others may prefer down does not move. When washing, the diamond baffles have less down per baffle, so there is less danger of breaking fragile baffle material by the wet down. On the other hand, every stitch is a point where there is no insulation, thus cold penetrates. There is a baffle system (used mainly in sleeping bags) where the the inner seam is slanted from the outer, so that there are no cold spots. This would be the reason to choose a horizontal baffle system over diamond. When looking at down jackets inspect the seams on the inside and outside and see if they are offset. If not each seam is a cold conduit.