*I keep 2 of these in my army. Because they burn buildings they can attack a building for 3 seconds and move on to the next before the building is even 1/4 damaged. If you have a lot of the defenses knocked out or if you are assaulting a keep and have most of their defenses are busy unleash the dogs of war and let them clear out their resources while you keep on clearing that path to the keep. Just remember when using them never assign them to attack a target, always point them in the direction you want, otherwise they stay on the building until its gone.
*(another player) I have 4 of these in my army,i keep them together and have them attack towers once the tower is occupied killing my other units,then they set the tower on fire,and after that the fire keeps burning until tower is destroyed or battle ends. Or i have them keep attacking the tower until its destroyed.