BeforeDestruction is called automatically immediately before the component's first destructor executes. Do not call it explicitly in your applications. 

As implemented in TComponent, BeforeDestruction checks whether the Destroying method has been called, and if not, calls it. Descendants that override this method to perform other actions before a component is destroyed should call the inherited method first to ensure that this check takes place. 

Destroy 

Destroying 

System::TObject::AfterConstruction