Continuity mistake: When The Bride gets into the Pussy Wagon and tries to move her toes, the shot changes between one taken from her head and one taken from her feet. The one taken from her head shows her two feet touching one another and resting against the closed door. The one taken from her feet (which would have necessitated the door being open) shows her two feet not resting on anything and slightly apart from one another.
Continuity mistake: When we see the Bride in the "House of Blue Leaves", her hair is considerably longer than when it was while she was walking through the Tokyo airport. Since we see from time to time in the movie, the notations "one month later," or "4 years later," and there was nothing like that in the sequence, it seems that the Brides' hair grew at least 4 inches from the time she left the airport until the time she gets to the restaurant.
Continuity mistake: When Vernita and The Bride are talking in the kitchen and Vernita shoots The Bride from the cereal box, you can see the bullet hole in the back wall of the kitchen, but then a little later that part of the wall doesn't have any bullet holes. Also, not only is the bullet hole not where you see it hit in the first place, it's on the other side of the bride's head, along with the splatter from the cereal box.
Continuity mistake: During O-Ren's speech the blood on her forehead changes between shots.
Continuity mistake: When O-Ren Ishii beheads Boss Tanaka, the bald boss sitting next to Tanaka alternates between holding a fan and not. After Tanaka's head is chopped off, there's a quick shot to bald boss to see his reaction, and he's holding a fan. When the shot goes back to him a second time, the fan is gone.
Continuity mistake: During the restaurant fight scene to get O-Ren, the blood on The Bride's face (particularly her nose) keeps changing. This may be an homage to older martial arts films, but at one point towards the end it is in the same spots as it was in the beginning as well.
Continuity mistake: When Gogo gets hit by her metal ball, she falls and breaks a table, and a lot of splinters gather around her head. In the next angle, for only a couple of frames, there are fewer splinters.
Continuity mistake: O-Ren shot the dart from where she was sitting in the private dining room at the restaurant. Since we see the dart travelling in a straight line past the kneeling Bride's face, the dart somehow manages to stop at eye level when Go-Go retrieves it.
Continuity mistake: When Uma Thurman is standing in the kitchen talking to Nikki, the position of the strap of her knife holster rides up and down her thigh between shots.
Continuity mistake: When O-Ren's young bodyguard has the mace, she hits the Bride smack in the chest more than once with the very heavy, spiked ball. But later, there is not a trace of a welt, bruise, or cut on the Bride's chest (plenty of blood on her half-zipped jacket but her skin is just fine.)
Continuity mistake: Oren is in the back of a limo, with all six motorbikes ahead of her, after the final two have moved up from the back to the front, but when we see a shot of Oren, in the limo, there are four headlights behind the limo, the way it was before the bikes moved up.
Continuity mistake: In the fight scene between Gogo and The Bride, keep your eye on the ball and chain weapon. It spins in different directions depending on the shot.
Continuity mistake: When The Bride and Vernita Green are in the kitchen, Vernita mentions something like "I've got to fix my daughter's cereal." Notice when she says this, The Bride is holding her mug with the handle facing Vernita, when the shot changes, it is instantly facing The Bride - something which cannot be achieved this quickly.
Continuity mistake: The Bride's face gets beaten up with visible marks during the fight with O-Ren's last female fighter. But after the fight her face is back to how it looked before the fight.
Continuity mistake: The Bride cuts off both of Sophie's arms, but when she throws her into the hospital, she has one arm. (This mistake is only seen in the extended Japanese version of the film - in other versions only one arm is cut off).
Continuity mistake: Tanaka's severed head lands on the table and stops rolling, meaning it should stop moving. However, it then falls off the table.
Continuity mistake: In the Crazy 88 fight, when The Bride stabs a bald Crazy 88 member, at first the sword is to the left of his tie, but when we see a closeup, it's to the right of it.
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.