Perplexing Tempest has two uses. 

First it prevents a strong counter-strike from your opponent's melee units:  You can play Tempest and newly summoned units can’t reach your units.
One of the reasons it is dangerous to not pressure Breakers is that it gives them space and time to set up a very good Perplexing Tempest, which can be a big turnaround point.

A turn where all of your units can attack and then your opponent can’t reach them, is a game-winning turn a lot of the time.

The second use is to make it harder for the opponent to retreat.  Sometimes you can maneuver Tacullu close to the opponent summoner, and as it would like to retreat, you can just play Perplexing Tempest and make that retreat very hard, setting up for a powerful Mind Control and/or other shenanigans for the kill.

If you can just prevent a single attack from happening thanks to Perplexing Tempest, then it's well worth it's use.