There are a number of useful things fire lizards can do in Dragonsong. As one might expect, fire lizards can breathe fire and thus can help humans in many useful ways, such as lighting fires for cooking, campfires, or torches. Fire lizards are also capable of cooperating with humans to accomplish goals, such as when the queen fire lizard allows Menolly to help move the eggs of her clutch to a more secure location.
Though it is not clear how precisely fire lizards can understand human language, their ability to cooperate with humans shows that they understand human motivations and can communicate indirectly via actions. With the ability to be "Impressed" by humans—a form of bonding—some "fire lizards knew what was in the mind and heart of a person." Menolly even manages to train fire lizards whom she has Impressed to sing, further showing the complex behavior fire lizards are capable of.
Though they are not big enough to carry humans like the dragons who fly with dragon riders, fire lizards are better suited for some tasks as a result of their more human scale. Fire lizards can carry messages around and are also said to be useful for exploration, scouting, and searching. Finally, loyal fire lizards will fight to defend those who have Impressed them.