About Section View Drafting Buffers
Section views are created with drafting buffers. When you add AutoCAD annotation or drafting elements or Autodesk Civil 3D note labels within or crossing the drafting buffers, they are bound with the section views, and are moved with the section views if they are moved.
AeccViewportOpt (System Variable)
Use the AeccViewportOpt system variable to control the behavior of viewports whose types are set to Section so that only the objects that appear within viewports are generated and redrawn.