In 1980 Steven Spielberg re-edited his original Close Encounters of the Third Kind dropping several smaller scenes and adding other sequences.
The differences between the various versions are too numerous to go into in full detail - especially considering that for network screenings of the movie all existing footage was used!
In the end the film is tighter in the midsection, but longer towards the end. In fact, the final scenes reveal a lot more of the interior alien mothership and while those new scenes are spectacular (the new effects were designed by the underground artist Ron Cobb - but no credit is given) they are redundant to a degree and tends to drag.