It gives you a peek at your top card and lets you play lands or bird spells directly from there, which keeps your hand flowing even when youre topdecking
Lets take a look at Lugia VSTAR [Silver Tempest] for example, you really need to get Archeops [Silver Tempest] out of your hand, so you can summon them with Summoning Star
Certain cards will grant energy counters which you can then spend for effects ranging from damage to buffs to card draw
However, it is still trumped by Mythical Island Raichu for just one extra Energy and no reliance on Arceus
After some months of testing though, it quickly become a frequently played mainstay in the format, and I already have in a lot of maindecks/sideboard of my decks
Eerie Ultimatum, one of the best Abzan cards, is a big source of card advantage in Abzan graveyard-related decks