You can toss away beefy threats in the early game to draw out weaker things you can play now, knowing full well that you can discard something else later to drag that bigger creature back from the depths of hell
Haste Cowards can't block Warriors
Its free and will give you useful information regarding your collection, suggest Draft picks, and will even try to predict what deck your opponents are playing based on the metagame and their known cards
Choosing a higher value for X lets you pay more mana and thus spend more colors of mana to cast it
"Everything the wise woman learned she wrote in a book, and when the pages were black with ink, she took white ink and began again." Karn, silver golem
While Im not personally a fan of the Tarkir: Dragonstorm Omen mechanic, there are plenty of Magic: The Gathering players out there excited to try it out