Sector fuel burn + payload = landing weight
Now if sector fuel is less, ie more fuel efficient due to better ATC routing, better winds and more economical fuel burn figures than predicted by Avnet, then there will be surplus fuel still in the tanks over and above that planned for, thats a good thing, but id your payload is at max..(ie v/good payload figures thus), then the aircraft will be overweight for landing, hence the wider routing required, or the lower less fuel efficient altitude required to get the actual fuel burn to match the planned fuel burn.