Gehemahnets work like a magnet for daemons of the Warp that are trying to break through the dimensional barrier between the Warp and realspace so that they can infest the newly conquered world. The barrier between the Realm of Chaos and the material plane are thin in the proximity of the Gehemahnet. Daemonic entities strain from beyond to cross the thin walls and enter the physical world. When the tower is finally completed the barriers are stripped away like flesh from bone and the daemons are able to take corporeal form and transform the doomed world into the latest incarnation of a Chaotic hell.