The balance of Power is a long quest in Legion. You will reward achievement "Improving on History" when finished the quest, and will unlock Artifact Appearance Valorous Style (Tint 1). The first Tint is the necessary condition to the three kinds of Tints, that is you have to unlock the first Tint, then have an opportunity to unlock the following three Tints.
Apparently, this questline begins when Archmage Kalec shows up to your class hall after you unlocked your artifact weapon's third slot. The balance of Power asks to pick up task items in Mythics, to earn Blood of Sargeras, to purchase task items with reputation, to unlock two mythic dungeons by doing Suramar questline, also to collect 30 Fallen Essence in The Emerald Nightmare(more than in Normal difficulty)... This is not the end, later still need you to complete questline in Nighthold. The balance of Power throughout all of the Mythic Dungeons and Normal Raid, such as the Legendary Ring and Legendary Cloak will not be completed at one time. This quest is a long challenge for players who love Artifact Appearance Valorous Style.
All the above is only to unlock one Artifact Appearance, worth it? Well, it's up to you. Of course, you will upgrade your item level a lot during that many of dungeons and raids.