Sometimes theyre valuable in terms of dollars, but its sometimes the sentimental value that means more
Ragavan is simply one of the best cards in Modern at the moment, and has plenty of decisions just because of the dash ability, nevermind whether or not you want to cast a spell from your hand or one from the top of your opponents library
Whether they supply blockers for Blinkmoth Nexus and Etched Champion, pressure to attack an opposing Liliana of the Veil, or simply Shocks on a stick to trade with various Humans, Elves, Merfolk, or Flickerwisps, Pia and Kiran put in the work you need in your Jeskai, Jund, and Grixis decks
Various builds of Landfall decks have existed, but the most common version seems to be Temur Landfall