It enables you to wear one less piece of your required 6-piece Set, allowing you to bring Captain Crimson's Trimmings.

The Ring of Royal Grandeur is the star of the show being used in all 28 builds.

The pieces are crafted at the Blacksmith and are used in nearly every Set Dungeon build.

Captain Crimson's Trimmings provide Cooldown Reduction, Resource Cost Reduction, Damage and Toughness.

In Season 25 we will avoid using Soul Shards in Set Dungeons as they are generally very powerful and can complicate some of the needed objectives. There are also specific Legendary items that are used frequently that can be reused as you move to other classes shown below. Being patient will help you complete many of the objectives so just take a relaxed approach, gather up the enemies for the objectives and you'll sail through. The last thing you want is to have to backtrack through the whole dungeon at the end to kill a few enemies you left behind.

Every Set Dungeon requires you to kill every enemy present so focus on completing the objectives early on while making sure not to leave enemies behind. Some can be easily failed if you have too much damage, Area Damage or even skills that kill things passively such as Mystic Ally or Gargantuan. None of them require amazing gear and can be completed with non-ancient Legendary Items, level 25 Legendary Gems, and zero Augments.

For 99% of Set Dungeons you want max Cooldown Reduction, Attack Speed and Resource Cost Reduction to cast your abilities faster and more frequently.

Wizard season 19 diablo 3