In short, you want to balance the mana value of your spells to ensure you have effective spells to cast throughout the game
Loxi: It's a storm card
Daybound and Nightbound promised a more dynamic approach to double-faced cards, flipping back and forth multiple times throughout a game instead of a single transformation
IGN: When I first looked at the cards in Set 1, I was surprised to see Be Prepared and A Whole New World because cards with those same effects were so strong in other TCGs that they wound up getting banned
Generally, ST11-001-uta players pick one of these as their big threat in the deck: OP04-031-donquixote-doflamingo, OP06-118-roronoa-zoro, OP01-051-eustasscaptainkid-701, P-061-monkeydluffy, and OP06-035-hody-jones
Thankfully, white gives players other opportunities to cast cards for zero mana