What architectural feature is a flying buttress primarily used for?

The flying buttress is primarily used to support the weight of a roof or vault. This architectural feature extends from the upper portion of a wall to a pier or support structure that is located away from the wall. By distributing the weight and the lateral forces created by the vault or roof, flying buttresses enable the construction of taller and thinner walls, which can include larger windows. This design innovation is most famously seen in Gothic architecture, where it allowed for the incorporation of stained glass windows and impressive height, contributing to the overall aesthetic and structural integrity of cathedrals and other large buildings. The other options, while they may describe architectural elements or functions, do not accurately represent the primary role of a flying buttress in structural engineering.