Even the best offensive magic is worthless if the true goal is to give the enemy a nasty surprise. In such cases, this spell is quite useful. Casting it on a chest or door puts a trap of varying effect (poison, acid, bomb or sleep) on it. Any foe who dares to touch it will get a nasty surprise when the trap is set off.
Note that to get rid of the spell, the Destroy Trap spell has to be used (also called "Untrap") to disarm the trap.