Would it be useful against Zekrom (since Ground moves are so terrible) and Kyurem (since other dragons would be glass cannons against it)? What about if Palkia returns?
Of course, it would be useless for Reshiram and Dialga, while Rayquaza is doubly weak to Ice. I suspect Terrakion may have too many better counters (likewise for Giratina).
Most Dragon-type gym defenders are doubly weak to Ice, but Mamoswine is vulnerable to Salamence (Fire Fang hurts and Hydro Pump is hard to dodge). Confusion is equally SE into Fighting-type defenders.
As for gym defence, I guess Charm handles attacking Tyranitars better (and attacking Metagrosses slightly less worse)?