Part of what makes playing Legacy so intricate is the subtle difficulty of maximizing the value of your cantrips. Brainstorm, Ponder, Preordain, and Portent all see play in the format and all do similar things, but those that recognize their differences and how those differences impact gameplay gain a small but significant advantage that compounds over the course of a game, match, and tournament.
Decks with a high density of cantrips and other velocity-granting effects are able to play preposterously low land counts for their curve, a principle first put into practice by Alan Comer and his Turbo Xerox deck over twenty years ago. Additionally, the increased consistency that's granted by seeing more cards than the opponent in an average game gives these decks a lower fail rate. And finally, they're able to diversify their cards, both threats and answers, and play more narrowly powerful effects (especially in the sideboard) and still find these cards consistently even when played in low numbers.
But these advantages can only be realized if the pilot leverages their card selection spells and other cantrips effectively. Every mistimed Ponder or Serum Visions might mean you miss seeing the extra card or two that could make the difference in a game.
Having played Storm in Legacy for a long time, I recognize the value in sequencing card selection appropriately, but never have I played a deck where it was so nuanced and important as it is in the list I took to a first-place finish last weekend at the StarCityGames.com® Open in Baltimore:
This list has twenty spells in the maindeck that can dig for more cards, and four of them come back from the graveyard for a second go. Among commonly played Modern decks, only Storm rivals it in terms of velocity and card selection. But in a format as fast as Modern, you can only spin your wheels with cantrips for so long before you fall too far behind to catch up. This deck is also trying to find and recur Arclight Phoenix or transform Thing in the Ice as quickly as possible - ideally on the first three turns of the game, so utilizing these cantrips to their utmost is essential to realizing the deck's full potential.