Extending or Extruding Surface Edges Examples

Pulling the edge of a surface up to another edge forms a solid if it closes the body.
Pulling the edge of a cylindrical surface extends the surface along a cylindrical path (A) unless you hold Ctrl (B).
Pulling the edge of a cylindrical surface with the No Merge option selected creates a new edge.
Pulling the edge of a cylindrical surface with the Both Sides option and holding Ctrl creates a new surface tangent to the cylinder and extends in both directions from the edge.
Pulling an edge with the Pivot Edge option.
Pulling an edge with the Copy Edge option