I think it's just for Devs ease. Instead of running scripts to give items to players, they'll just display on everyone's screen: "Type IDDQD code for bonus premium item!". You type it and - BAM! - you get 10 Duel Banners! Yay! Then again, you see: "Type IDKFA code for another outrageous premium item!". You type it and - BAM! again - you get 3 Fireworks! Woohoo!