Wolfram Technical Support, Andrew Lewis, answers:
... Specifying a 3-D point as either a Prolog/Epilog in Plot3D would
make sense programmatically, but it would not make a difference to the
overall graphic when compared with using the Show function with Plot3D
and that same 3-D point.
However, I have sent a suggestion report to the appropriate people in
our development team so this can be considered for future versions of
Mathematica. ...
Thanks to Andrew
