Originally Posted by
lwalker8
In a word, burst.
It was very much irrelevant until the Shadow 4 piece set came out for the current tier. Making the combination of shadowfiend, dark evangelism and mind spike and mind blast a very potent burst over 15 seconds.
Obviously this was done by the developers in recognition of the fact that we lacked a burst damage mechanic and such a mechanic was necessary for some of the heroic mode encounters in Dragon Soul.
Prior to this tier, it was used basically as a way to remove DoT spells quickly from a target, such as on Omnitron. It was also common to use mind spike on trash.