Trivia: The radio station that the sheriff is listening to, while driving to the murder scene, is KTRN radio in Wichita Falls, Texas. This radio station was also used in the movie The Last Picture Show. However, that radio station doesn't exist anymore in Wichita Falls.
Trivia: When the Bride calls out for O-Ren at the House of Blue Leaves Restaurant after encountering Sophie, she yells O-Ren's name out, followed by the phrase explaining that they had unfinished business. This was all in Japanese, since there were subtitles present on screen at the time. However, traditionally when speaking someone's name in Japanese, the last name comes first. (i.e. Ishii O-Ren)
Trivia: The character Gogo was originally written as two characters: the twin Yubari sisters, Gogo and Yuki. Gogo had almost no lines and after her death at the hands of The Bride, Yuki would seek her out, only to be killed as well, in the "lost" chapter "Yuki's Revenge". All of Gogo's dialogue would have been spoken by Yuki. Tarantino references this lost character/scene in the first chapter of the movie; when The Bride is standing outside of Vernita Green's house, you can faintly hear an ice cream truck jingle. This was originally supposed to be Yuki, who stalked The Bride in an ice cream truck.
Trivia: The vengeance music/siren shows up three times in this film: when the Bride shows up at Vernita's door, when the Bride is confronting O Ren, and when the Bride spots Sophie. Strangely, Sophie never injured the Bride during the massacre scene. This sound only shows up once in Volume 2, when the Bride spots Elle and Budd at his trailer.
Trivia: During the scene at the House of Blue Leaves, right before The Bride cuts off Sofie's arm, she tells O-Ren that they have "unfinished business." The close up camera angle of The Bride's lips is the same angle Quentin Tarantino used in "Pulp Fiction" when Mia told Vincent (through a microphone) that she'd be down "in two shakes of a lamb's tail." (01:13:35)
Trivia: The Kill Bill series was originally supposed to come out in theaters as one movie. But it was too long, so the directors decided to cut the film in half and make a "two-parter".
Trivia: Since this movie is supposed to be a tribute to old kung-fu movies, spaghetti westerns and other B-movies, many of the mistakes may be intentional to add to the "low budget movie" feel.
Trivia: Sofie's cell phone ringer, along with Elle's, is the first line to "Auld Lang Syne" or "Should auld (old) acquaintance be forgot."
Trivia: You may have noticed that the Texas Ranger who is in charge of the 'wedding slaughter' also stars as a Texas Ranger of the same name in From Dusk Till Dawn, another film written by Tarantino. He dies in that film, suggesting that the films occupy the same "universe", and this film is set before From Dusk Till Dawn.
Trivia: In the scene when O-Ren is walking with her gang into the restaurant (towards the end of the film), her obi (the belt of her kimono) was tied too loosely and too low as well. This may be because she is going to be a doing a fight scene later, but Japanese women do not tie their obi in that way.
Trivia: During filming, the actors would often provide a "Hello, Sally." take. This involved the actor finishing his or her take, turning to face the camera, and yelling "Hello, Sally.". Whether or not editor Sally Menke actually appreciates this has yet to be reported.
Trivia: In a scene at House of Blue Leaves that includes O-Ren and Sophie, one of the gang is on his back telling a risque story that is not translated. What he says is exactly what he is miming. (01:09:15)
Trivia: The "Man from Okinawa" is played by Sonny Chiba, a famous martial arts actor in many of the films that Quentin Tarantino used as inspiration for Kill Bill. In True Romance (written by Tarantino), a man loves kung fu movies and is going to see a Sonny Chiba triple feature for his birthday.
Trivia: The psychedelic swirls at the beginning of the film stating "Our Feature Presentation" was common at drive-in theatres of old.
Trivia: The original script featured the Bill character to be a master alchemist. The liquid in the syringe was pointed out to be a concoction created by Bill entitled "Goodbye Forever". These potions/elixirs were to be detailed by on-screen subtitles. The Bride would also use a mix called "The Undisputed Truth" to get information from Sofie Fatale.
Trivia: On the DVD cover for Kill Bill, Vol. 1, Elle has her eyepatch over her left eye, when in the movie the patch covers her right eye. (00:19:20)
Trivia: Buck is based on a character played by Robert Englund in the 1977 movie "Eaten Alive" in which he says "My name is Buck and I'm ready to F**k."
Trivia: At the beginning of the scene where the sheriff walks into the church after the wedding massacre, there is music playing. When the singers say "Donde esta.." there is a static sound like a radio changing station. Quentin used this same sound effect in the opening credits of Pulp Fiction to change from "Misorlou" to "Jungle Boogie".
Trivia: Sophia was also a name of one of the Fox Force Five girls in Pulp Fiction.
Answer: From what I understand the reason for the lights being off is the same reason for why the previous scene was done in black and white; to decrease the amount of 'graphic violence' in the movie in an attempt to keep an 'R' rating. I would assume that they had him shut off the lights for that scene as just another method to accomplish that task.
I believe the original question was asking why was it done within the context of the film (i.e. why did the character shut off the lights) not why was it done in reality. My best guess is that the manager switched off the lights thinking the 88 had a better chance of killing the bride if she couldn't see. True, they couldn't see either but there were so many of them one could possibly have gotten to her.