Exposing a 2D component lets you cut any existing link between a 2D component
instance and its reference in a catalog, by creating (from the reference
in the catalog) a 2D component reference on a detail sheet.
In a given representation, all 2D component instances linked to the former
catalog reference are then linked to the exposed 2D component reference.
This also allows you to modify the 2D component reference locally (without
modifying the catalog reference).
Nested 2D components
Exposing a 2D component instance creates a unique 2D component reference
with no 2D component instance inside, even if the original 2D component
reference contains several 2D component instances.
Refer to About 2D Components for more information.