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.
The musical provides examples of:
Big Lipped Alligator Moment: Both the songs Never The Luck and Off To The Races come out of nowhere and add nothing to the plot, and neither does "Wages of Sin." It was just a popular song for Angela Prysock.
Crack Pairing: The 2013 Broadway revival album includes the "Perfect Strangers" reprise, whose participants are selected by the audience each night. Setting aside the fact that the evening's murderer is ineligible as they've already been clapped off in irons, there are 21 possible combinations (three women and seven men). How did those in charge of recording the album decide to work in this song? By dividing the lines up among three of the crackiest pairings possible: Deputy & Puffer, Neville & Helena, and Durdles & Rosa. They knew their audience.
Nightmare Fuel: A fair portion of the book, but the scarab Drood puts in Wilkie's chest and the spirits (or whatevertheyare) that live in Wilkie's house, particularly Other Wilkie, are probably the shining examples.