Cinders drop in Helltides and are used to open Helltide Chests, which offer the best gear in the game.
Diablo 4 has a multitude of Gold sinks, including Enchanting and Upgrading items, and buying items from vendors.
Red Dust is the purified form of Seeds of Hatred and is used to buy cosmetic PvP rewards, like Armor and Mounts.
Seeds of Hatred
Seeds of Hatred drop on the Fields of Hatred from slain PvP opponents, monsters, etc. and must be purified.
Multiple currencies for different uses
In Diablo 4, players collect a handful of currencies, some only available in specific areas, like Cinders in Helltides and Red Dust in the Fields of Hatred. Gold is used in the purchasing of most items and services, and feels more valuable in Diablo 4 than in past games in the series. Enchanting affixes on end-game items costs hundreds of thousands of Gold.