If you are playing with Zerg and especially you are playing against Protoss race.The usage Ultralisk will be very efficient because it has a very strong armor,high amount of energy and relatively strong attack capability.These monsters can be used to overcome the main Zealot problem in the combat.It has high cost but it gives very precious advantages to the players.Mass dragoon tactic may stop these creatures invasion but if you use them with lots of Zergling or by Defilers these photon sources will mean nothing against these beasts.But be carefull every warmachine has a predator in Starcraft Universe.The Ultralisks can be defeated by Dark Templars (because of superior Warp Blades) or can be eridicated by Archons which has splash damage capability will truly harm the Zerg Swarms.Of course Protoss Rockss! .