Bonus rolls are provided by Seal of Broken Fate in World of Warcraft: Legion. You can obtain several of these from Archmage Lan'dalock in Dalaran near the entrance to Violet Hold.
 
 The pricing for these Seal of Broken Fates is as follows:
  • Gold: 1,000 -> 2,000 -> 4,000
  • Order Resources: 1,000 -> 2,000 -> 4,000

The pricing for each of the above resets on a weekly basis. For example, at the beginning of each week you can obtain two bonus rolls by spending 1,000 gold and 1,000 Order Resources.
Bonus rolls allow you to re-roll for drops on raid bosses, providing a means of gearing up quicker.