can somebody explains the need for having 2 properties for drag behaviour?

The docs state:

allowDrag : Boolean
False to make this node undraggable if draggable = true (defaults to true)

draggable : Boolean
True to make this node draggable (defaults to false)

So if I want to make a node non-draggable, I would just set 'draggable' to false. So why would I ever need 'allowDrag'?