It's an extremely devastating weapon. Just today I used it four times to great effect in two different games.
The first was with my friend, a 2v3v3 against AI teams on a 3-star map. As we cleared our starting star system, I asked my friend to have control of the only planet directly connected to the sun so I could Wail any incoming armadas from the other systems if need be.
Later in the game, when the AI were in ruins and it got to the point where it was just a big mop up operation, we turn on each other and he swarmed me with massive amounts of bombers in the second system. After I retreated, his ships fled from my Eradica which had activated Unyielding Will and I lost track of his fleet.
Until I spotted his entire drone host fleet jumping to the other star, at which point I waited for all of them to arrive, then hit Wail of the Sacrificed on the one planet next to the star. My friends parents entered the room and asked to use the computer for a few minutes and he requested a break, to which I answered:
"Sure, since I just obliterated all of your carriers, we can take a break"
He begins to panic and I hear him hitting his hotkeys looking for his carriers.
He is still relatively new to the game and didn't fully understand how Wail worked. Now he does.