What was the importance of the Ardennes Flank, a French Campaign in May 1940 as noted in the biography, Adolf Hitler?

A key feature in Hitler's attack in the west on May 10, 1940 is the Ardennes Flank. While the German army attacks Holland and through Northern Belgium, Allied armies are led north along the English Channel. Then, on May 13th, German forces attack in Southern Belgium, at the start of the French Maginot line. German forces penetrate to Sedan, and then are able to cut off Allied forces as they drive towards the English Channel from the South. The French defenses are totally outflanked and destroyed, and soon France surrenders.