It is even more powerful if you place your Roaster and/or Air Bombs near the Builder Hall, which can quickly overwhelm enemy air troops. This will disrupt any enemy Air Troops which approach your base from that corner. Put Mines (in air mode) around your Builder Hall if it is located in a corner.
When set to Ground mode, it can stop a mass of Skeletons spawned by Drop Ships but only if other ground units, such as the Battle Machine, trigger the trap.