Holy cow, I wrote a book!
A customer wanted to know how to
get the effect of
on a window that already exists.
In particular, they wanted to be able to reposition a dialog
box to get the
CW_USEDEFAULT cascade effect,
but since you can't actually pass
CW_USEDEFAULT in a dialog template,
the repositioning has to be done after the fact.
(Presumably in the WM_INITDIALOG handler,
which runs before the dialog is visible,
so that there is no visible flicker.)