I don't know what you mean by "that are not used". The only reason those parameters would not be used is that you are not referring to them in your code for evaluation of the Shift key or mouse position relative to control at the point of execution.
So, go ahead and use them if you want, example:
Private Sub OptionButton1_MouseDown(ByVal Button As Integer, ByVal Shift As Integer, ByVal X As Single, ByVal Y As Single)
Dim ShiftSpeak$
If Val(Shift) = 0 Then
ShiftSpeak = "your keyboard's Shift button was not pressed."
Else
ShiftSpeak = "your keyboard's Shift button was pressed."
End If
MsgBox _
"When you clicked the mouse," & vbCrLf & _
ShiftSpeak & vbCrLf & vbCrLf & _
"Regarding the mouse's location relative to OptionButton1:" & vbCrLf & _
"Mouse position as distance from left: " & Val(X) _
& vbCrLf & _
"Mouse position as distance from top: " & Val(Y), _
64, "MouseDown info for OptionButton1"
End Sub