You can unlock additional visual effects for Vault of the Incarnates Tier Sets in Dragonflight through Mythic+, raiding, and PvP.
Deep Cuts From the Vault is a new achievement added in Dragonflight Beta Build 46420, which rewards Gleaming Incarnate Thunderstone upon completion. The item unlocks additional visual effects for Vault of the Incarnates class set appearances.
Once unlocked, the effect is account-wide.
Blizzard has not specified what visual effects are, but we assume it’s the various helm/shoulder effects found on Mythic difficulty and Epic PvP sets. Below we show you the Heroic and Mythic versions of the Death Knight tier set. As you can see, the Mythic shoulders have an additional visual lightning effect. Maybe the item will make those available on gear regardless of difficulty.