Well, they're not important enough for MS to remember to
include them in the documentation or to keep the
documentation up to date with reality.  Remember that MS's
position is that if it's undocumented, they can do whatever
they want with it, including throwing it out or using it for
some entirely different purpose.  If they failed to fix
their code to reflect the documentation, that's their
business, whether we agree with it or not.  The fact that
neither of us has found a use for them just adds to the
argument's weight.

I suppose that you could think of them as the original
designer's assumption that there should be parallels to a
form's Open/Load and Close/Unload events, but that there is
no need for those callback hooks in real situations.

I guess I should have provided an expanded explanation in my
original response.  I went through the same kind of
exploration of this feature several versions ago and came to
the bottom line conclusion that I posted earlier.