The article examines the widespread practice of using extended judicial formations to decide certain types of cases in higher courts, a practice present in many jurisdictions—whether appellate, apex or supranational. While the use of these formations, often considered the ‘most important’, is frequently debated within individual countries, a conceptual and comparative analysis providing a firmer theoretical foundation for these discussions is currently lacking. Departing from existing scholarship, which often assumes a universal purpose for these bodies, this article argues that jurisdictions tend to adopt one of two models of extended formations: the collective control model or the jurisprudential model. These models reflect divergent sources of legitimacy for the enlarged formations—either rooted in the broader participation of judges in the court’s decision-making process (input or procedural legitimacy), or in the doctrinal quality of the decisions that the grand chamber produces and their resulting consequences (output or performance-based legitimacy). These distinctions help to explain differences in how extended formations are composed, the types of cases they hear, the procedures they follow and how their decisions are drafted and subsequently used within the court. The article ultimately demonstrates that the choice between the two models reflects broader assumptions within different judicial systems about the nature of law and judging.