Some of the coin buffs are actually insane and change shit like crazy. For example, one coin changes every single operator's skill into offensive recovery for a floor and then all offensive recovery skills gain 2 SP on attack. There's a coin that gives you 3 speed for every 2 ingots. Coins are consumed at the end of the floor and turn into a worthless form. You roll new coins at the start of each floor and equip 3. You can also get coins that grants only debuffs (you want to trade them away as quickly as possible) and coins that offer both debuffs and buffs (e.g. all enemies have -45% HP but your ops have -25% HP)