I recommend it as an anti-assassin soul skill. If you've got a dragon on the field and the enemy has a dead unit and has been keeping a shade or something alive on the back row (or otherwise telegraphing an assassin sacrifice maneuver, Use Petrification on your own dragon. It'll make him immune to the Assassin soul skill, and protect him from most attacks for the turn as well.
"Scissors are overpowered. Rock is fine." -Paper