Which statement about levels in Revit is true?

Levels in Revit serve as reference points that establish the vertical positioning of elements within a project. They provide a way to define heights or elevations for various components such as floors, ceilings, and roofs. This hierarchical representation of vertical space helps ensure that all building elements align correctly concerning one another, making levels vital for accurately modeling a project.

The other statements do not hold true. For instance, levels can indeed be edited after their creation, allowing users to adjust them as design changes occur. While levels provide important reference points, they do not define wall thickness; rather, wall thickness is typically specified through wall types and properties. Additionally, while levels are essential in various contexts, including structural, they are not limited to structural elements. Levels are widely used in architectural and MEP (mechanical, electrical, and plumbing) components as well.