What are the hide windows in frame.c?

[Viktor Griph]

When are the hide windows useful in frame.c? The call to 
frame_reparent_hide_windows in frame_create_move_resize_args casue X to 
generate extra VisibilityNotify events to clients during capture and 
redecoration (bug #3977). Would it be possible to narrow down the need for 
that function call to some specific case?

/Viktor