its more than likely not more fuel efficient.
But instead of having 2 sectors of approach controllers and one Director or what ever you want to call the position that hooks them off the down wind and merges them onto finals you can get rid of 2 controllers and just have one doing the whole lot.
Of course once it gets implemented and the head count drops and the airlines start bitching about the increased fuel costs. The airports say sorry no can do we only have enough controllers to do it this way and it will take 2 years to increase our head count etc etc.