Last time I used it, it caused all my party member’s HP to go down to 1 and some of them lost all their MP as well. I thought: that’s pretty rubbish for an ability. Am I supposed to cast it at the enemy or something?
From the Ultimania:
It will do one of three things to each member of your party:
1. 30% chance it will fully restore HP/MP
2. 35% chance it won’t do anything.
3. 35% chance it will reduce everyone’s HP/MP to one
Why it might be helpful? ("MIGHT" being very subjective… XD)
There are also situations where putting party members at critical HP could be beneficial. In last-ditch efforts, combine this ability with Steiner’s "Charge!," which will cause any critical party members to physically attack the enemy. (up to 4 hits in one turn can sometimes be a good thing.)
If Quina’s in battle, there might be a chance to reduce his HP to 1, and, given auto-regen isn’t activated, if you have the Limit Glove magic, you can cast that for quad-9 damage.
And for other people: You could use this section to ask about other abilities (other than six dragons). That’s why I titled the section "FAQ on Abilites". Fire away!
Don’t let it stop you from using other anti-damage abilities, though, since it only kicks in AFTER the battle is over.