The Link function allows for creation of hierarchies that can be useful e.g. for scene optimization.
After the Link function has been activated, selected objects can be linked to some other ones. The objects the have a child-parent relationship, where the child is the dependent object.

Each child can have only one parent object. This means that if you try to link one object to more parents, the engine will "remember" only the last linking action performed.

The Unlink function cancels the Child -> Parent link.