As per http://www.beaucerons.net/history.htm 

"One of the essential breed characteristics, and a topic of endless debate in Beauceron circles, is the standard's call for rear double dewclaws.   The standard states:  "Dogs otherwise well qualified as to type but lacking double dewclaws can take only a mention."  There is a curious, somewhat superstitious, tradition attached to the presence of double dewclaws.  Old time ranchers believed that you could select a good working pup from a  litter by picking the one with these double appendages.  Indeed, this contention may have led to the establishment of this trait in the first place.  Some old timers believe that the double dewclaws allow the Beauceron to more easily climb onto the backs of the sheep.   Others point out that there is little muscular control the dewclaws, and that other breeds, such as the Australian Kelpie, are very adept without benefit of double dewclaws.   There was, in the past, a heated debate on this subject, when the Federation Cynologique Internationale proposed eliminating this requirement.  The parent club, in France, firmly held that without double dewclaws  the dog could not be considered a Beauceron."