Whether you realize it or not, as a writer you make promises to your reader. If you are writing a category romance, you promise a happy ending. When writing a suspense novel, you promise moments of tension so tight that the reader's palms should sweat. And so on.
But beyond the overall promise that a particular genre offers, there are smaller promises, too. Like the one - perhaps - on an author's page 6 which mentions in great detail, candlesticks. Why candlesticks? The reader will remember this for some time, that you spent great effort describing the objects. And if by the end of the book, candlesticks never factored into the story again, the reader will wonder why you bothered to mention them on page six.
Does this mean that you cannot mention any detail at all if not returned to later? Of course not. But what determines a "promise" is precisely the amount of detail you include early on. In other words, don't mention a gun hanging over the fireplace with intense writerly focus, if you don't mean to use it by the bad guy forty chapters later.
Readers love looking for "red herrings", even if you're not writing a mystery. They also like noticing "flaws" - you know, those kinds of images you eventually deleted out of the first draft, yet still remain with ghostly presence in the final draft. Things like three men at the shootout in chapter 14, scene 1, yet now only two men by the time you arrive at scene 2. The reader will go, "Huh? What happened...I thought there were three men?" They then spend several minutes flipping pages back and forth, trying to figure it out.
You might not notice the error, because your mind now has a reason for only two bad guys. But if you don't closely edit out your adjustments, you leave the reader confused - due to poor editing - and perhaps even worse, disappointed - when too much was made of an object early on in the story, never to be revisited again.
None of us like unfulfilled promises. That's why as writers, we seek only to emphasize elements in our stories that hold promise ... and make sure to revisit them when it really counts.