wxSizer: Define sizer hierarchie before putting controls in or vice versa?

[Piet]

Hello,
I have a short question about sizers and how they work when I have a
frame or panel with a complex sizer hierarchie. When creating a new
sizer which sits itself in its parent sizer, should I add the new
sizer to the parent sizer and then populate the new sizer with its
controls (some of them might be sizers on their own) or should I
populate the new sizer with all its controls before I add the new
sizer to its parent sizer? Or doesn´t it make any difference and all
the sizes and sizers are calculated anyways when the
wx.Window.SetSizer(wx.Sizer),wx.Window.SetAutoLayout(True) and
wx.Sizer.Fit(wx.Window) functions are run before before the window is
finally made visible?
Thanx in advance 
Peter