Allometries and scaling relationships have become popular among biologists. One reason for this popularity is the generality of these relationships, which has provided authors hope that allometries and scaling relationships represent biological laws or explanatory generalizations. In this article, I discuss three roles of allometries and scaling relationships: the explanatory, the predictive, and the heuristic. I argue that allometries and scaling relationships often function successfully heuristically—that is, discovering or elucidating patterns from data rather than making accurate predictions or giving illuminating explanations. The heuristic role is not to be overlooked. A science or discipline without interesting objects of explanation lacks the potential to progress and mature.