This talent is useful for PvE mainly for its reduction of cooldown on the Shadowfiend ability. With threat being practically a non-issue in the current game, the reduction of Fade in PvE becomes less attractive but if a priest finds themselves with mana issues, the reduction in Shadowfiend would be useful.
The reduction in cooldown of Fade is a useful component in PvP environments since Fade now provides mobility and escape. Being able to escape more often can save ones life.
Patch changes
/Patch 4.0.1 (12-Oct-2010): Moved from tier 4 to tier 1.