My aide asked me this question and made me feel old.
You see, children, we geeks used to go to opening night not for the prestige or because we were afraid of spoilers but because of the film.
By which I mean the actual physical roll of film which the studio shipped to the movie theatre in order for the theatre to show the movie. An actual canister of actual film, about the size of a large pizza box. Usually two per feature film.
Now, this is where you children will need to use your imaginations. The film was strips of celluloid run through a projector. Each time the film was run, tiny specks of dust and hair would get stuck to the celluloid. Sometimes the celluloid would rip and have to be repaired. And sometimes you got a moron who didn't notice the film had jammed and it burned away under the heat of the incandescent bulb (because we also didn't have LEDs yet).
Mostly though, the film just got dirtier and dirtier with each showing. Specks and blobs would flash up on screen, sometimes distracting us from crucial special effects or witty dialogue.
So we went to opening night, to the first showing, because that was the cleanest showing of the film. The closest to the director/writer/producer's vision.
With digital downloads to the theatres, this is no longer a real issue.
Now go forth and play with your pocket computers while I try to decide whether or not to yell at the kids to get off my grass.