Once youve decided to turn your creature face-up, you pay your cost and its face-up with no opportunity for your opponent to stop you
Combine that with ETBs that do stuff when a creature enters, and you can gain infinite life or do lethal damage
Or, alternatively, you can just animate Shorikai with Mobilizer Mech, Peacewalker Colossus, or Katsumasa, The Animator
Outside of a few copies of Sheoldred, the Apocalypse, the mono-black Waste Not decks of old ran few ways to actually close games that didnt involve Waste Not
I actually put Snapcaster Mage on 5 and think the card is a little underplayed especially in combination with newer cards like Counterspell, DRC, Unholy Heat and also Lurrus of the Dream-Den