You can't attack or block with a Planeswalker, but they're also not affected by summoning sickness and can use their Loyalty abilities as soon as they enter the battlefield
Chandra, Hopes Beacon Chandra, Hope's Beacon provides spellslinger decks a devastating top-end card
Most of the Jeskai Tempo decks only play two copies of Sarkhan, the Dragonspeaker as their planeswalker with the occasional deck playing one or two copies of Chandra, Pyromaster along with Sarkhan
The synergies that defined each 2-color pair varied, with some remaining the same, like Gruul Werewolves, and others shifting completely, like Orzhov Tokens vs Orzhov Lifegain
Its a subtle fluctuation but when the prices are as close as these Mox tend to be, any change is worth noting
It will be good in any deck with eight Plains, and every Mount creature you have in addition to that simply makes it stronger