With the return of Tier Set bonuses in Patch 9.2, some players are facing a new problem due to the conflict between new tier set items and legendaries which can only be crafted in tier slots. Although the legendary system was designed to be flexible, so that players could decide where to craft their powerful items, it wasn't designed around the idea of item slots being locked by specific pieces of gear — as we saw with Domination Sockets in Patch 9.1, some players will be faced with tier drops in slots they already have legendaries in, making them choose between their legendary and a two or four piece set bonus.
While eventually you may collect the four set pieces necessary to gear around your legendary, this requires players to either wait to craft that legendaries until they know which pieces of gear they'll be using, or continually recraft their legendary item(s) to avoid conflict. There is a point to be made that players could scrap their legendary using the new system added in 9.1.5.
However, this method only returns the currencies used in the craft, players would still need to pay the hefty cost of a new base legendary piece, which can cost over depending on their realm. This issue will be lessened once players are able to craft tier in other slots using the Creation Catalyst, but this will only happen 8 weeks into the patch.
This issue doesn't affect all legendaries and not even all specs. However, there are some popular examples like:
Echoes of Great Sundering for Elemental Shamans — Shoulder or Hands Freezing Winds for Frost Mages — Head or Hands Shadowflame Prism for Shadow Priests — Head or Hands Malefic Wrath for Affliction Warlocks — Shoulder or Hands Enduring Blow for Arms Warriors — Head or Belt (Conflic. Read more on wowhead.com