What is the difference between wParam WM_NOTIFY and idFrom in NMHDR?

The documentation for WM_NOTIFYsays :

• wParam:
  Identifier of the general control sending the message. This identifier cannot be unique. An application should use an element hwndFromor idFromstructure NMHDR(passed as a parameter lParam) to identify the control.

And the documentation for NMHDRsays :

• idFrom
  The identifier of the control sending the message.

What is the difference between the two?