These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Big Lipped Alligator Moment: In the movie, and of the non-comedic variety. While Arthur is busy waiting for the Woman in Black to acknowledge the discovery of Nathaniel's body, Mr. Daily has a vision of his son Nicholas which leads him to a tea room, where he's suddenly trapped by the ghost children and sees a ghost child make a creepy face at him outside the window. Then the main plot resolves itself upstairs and the door unlocks itself, letting Mr. Daily go free. But since he was already waiting downstairs with nothing to do, this scene changed nothing, accomplished just as much, and was never mentioned again.
Debatable. It could be a means of isolating Arthur and keeping Sam Daily from running upstairs and saving him.
Or it was Sam's son luring him into the room in order to protect him from Jennet, since Nicholas' ghost had a connection to his parents that none of the other ghost children displayed.
Idiot Plot: You're there to sort through the woman's paperwork, Harry Potter. Why not just take the paperwork back to town instead of staying in the house?
He was trying to figure out if the ghost truly existed. He did say, in a talk with Sam, that he hoped to find proof of the afterlife, but he had been disappointed when attending to a seance (as hinted by him looking at a seance announcement in the papers, during the train ride). Plus, it seems like there's, once again, a large amount of papers scattered through the house, which is abandoned and a thorough mess. He would most likely waste several hours, if not some days at least, to try and find it all. The most practical thing he could do is stay in the house till he finds everything (though one would call some help in such case, to search and organize the paperwork faster).