They bring consistency and balance to combo and control decks which have to have certain cards at certain times
The deck starts by casting strong Ally creatures with powerful abilities
Suddenly you have two different cards and effects on a single piece of cardboard, and although the new aesthetic of the split cards received mixed reactions, the gameplay more than made up for it
Lastly, there is a Chocobo-themed box with plenty of goodies for fans of either game
With double sleeving your cards are saved because the liquid only gets into the first layer and you can pull the outer sleeve off, saving your precious cards
Plus, theres the fun of meeting and mingling with other players while participating in prerelease events or different game nights for Modern, Standard, and Commander