Why bother ever playing with pesky lands when you could just have what you need in your opening hand
While it can be dealt with cleanly by a Swords to Plowshares, assuming you managed to hit a creature or planeswalker of theirs, they would have paid three cards (Swords, discarded card and creature/planeswalker) for your one (Entomb/Faithless Looting and reanimation spell offset by drawing a card)
The casting cost isn't ideal, but under the right conditions, it can lead to a big blowup by stealing one of your opponent's best creatures to use
Like most Magic: The Gathering cards, the value of Jenova, Ancient Calamity // Jenova, Ancient Calamity depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Final Fantasy Art Series)