Katara's waterskin ensured that she would always have water for bending, healing, or drinking
For a deck with Sazh's Chocobo, Mightform Harmonizer, and Earthbender Ascension, the interaction with Erode turns the card into a tactical Giant Growth (or more), especially when you are attacking with multiple Landfall Creatures
When one of the pieces of those combos is in your command zone , thats a recipe for consistency
In fact, the worst example so far was seen back in April, when some lucky players were opening a Fallout Mana Vault rather than Codex Shredder or Wastes
Its everyones favorite monkey and Magic's best 1-mana commander: Ragavan, Nimble Pilferer