Aside from unlocking events/getting mystery gifts, things not directly related to the Pokemon (berries, hold items, rare candies), and maybe Pokemon that were breed from a hack encountered Pokemon (I can make it work with Pokegen, not sure about AR codes)... AR codes aren't very good for passing a Pokemon as legit.
Everything in life is a battle. Even peace itself is a battle to maintain it.
You do realise TC is using an AR not PokeGen? General AR codes like the 'Make X Pokemon appear' and 'All Pokemon are Shiny' codes are 'dirty', they create corrupt Pokemon that wouldn't pass even the limited hack check of the past official tournaments, let alone the more strict one being introduced for X and Y.
I guess I should have clarified the "good hacks" in that last sentence. Even though I spent the first two paragraghs talking about it. Right AR codes are not good enough. But he was just talking about it in general as well.