Placing on a corpse that might get reanimated or ragnarok'd. Blocking movement, spawning or building especially in watery maps. Blocking Planar Rifts. Walling in Shield Generators or anything else that you want walled in, or closing some gaps of 1 space for shield generator contiguity or Lightning Bolt contiguity when there is an Awaken the Stones in play.
This is one of those cards that would be very useful in some situations, but most of the time just wastes card slots.EDIT: the shield generator contiguity thing won't work since it's uncontrolled.