Binding model nodes - seeming repetition?

Hello,

When creating a WD app using Adaptive RFC Model (or any model I assume), it is necessary to create a data link between the Model and Component Controller. Visually, the fields of the nodes of the Model and the fields of the model nodes of the Controller are linked. Why, then, is it necessary to again bind the model node of the Controller to the model object using the ".bind" method?

Code as shown here is a classic example:

	Bapi_Usr01Dohr_Getemployee_Input bapiInput = new Bapi_Usr01Dohr_Getemployee_Input();
	wdContext.nodeBapi_Usr01Dohr_Getemployee_Input().bind(bapiInput);
	bapiInput.setId("MY_USERID");
	try {
		bapiInput.execute();
	} catch (Exception exc) {
		IWDMessageManager msgManager = wdComponentAPI.getMessageManager();
		msgManager.raiseException(exc.getMessage(), true);
	}

Clearly the visual binding in the diagram view of the component controller and the programmatic binding using the .bind method of the model node are doing different things. My question is, what is the difference? Why are both required?