I leveled hammersmith for stormherald, and never done this quest.
So i checked wowhead, and this quest gives you the quest Expert Blacksmith! NOT the skill expert blacksmithing.
The only reason i could see was for the trinket that summons the Hammer of Expertise. A lvl 40 1 handed epic mace, 2.1 speed and 36.9 dps. Although, it's a summoned item lasting 1 hour, with a 3 hour cooldown.