IOTL, the French 7th Army, stationed on the far left of the Allied line, was initially intended to be held as a strategic reserve. In a rather foolish move, the Allies adjusted their plans and elected to send the 7th Army into southern Holland in order to assist the Dutch.
WI the Allies had held to their original ideas and kept the 7th Army in reserve rather than sending it off on a wild goose chase. Could it have been used as an effective counter attack force against the German bridgehead at Sedan? Could it have counter attacked the German right flank after the Sedan breakthrough?