I've been reading, and one of the books I chose, while the story is good, suffers from unnecessary detail. As a story teller, when you tell your best friend "what happened when I went to the fair" or some other event that happened in your life, you leave out the things they don't care about. You'll tell them about the concert on the main stage, about the rides and games, about the livestock, if applicable. You're not going to tell them you left the fair and had dinner in town (unless that's relevant to the fair for some reason, say "and then I saw one of the clowns, in costume, at the restaurant!") If I was telling my girlfriend a story and stopped it to tell her about a side trip into town to shop, she'd very impatiently ask me what happened at the fair, tell me to get out of the weeds in order to direct me back to the topic at hand.
While background information and a character's history, or backstory, is important to a novel, when it doesn't advance the story forward, it can be the difference between someone who reads a novel in one sitting and someone who might take days to slog through it (or decide not to finish it because the author keeps straying from the action). If the proverbial restaurant doesn't have anything to do with advancing the plot, leave it out of the story.
When I'm writing, I often suffer from "author intrusion"— information I need to tell the story, but which the reader doesn't need or want, at least not all at once. It can be drizzled in a little at a time, but an "info dump" will take you out of the story at hand. An example?
She heard a bump in the basement. "Is anybody down there" she called down the stairs as she flipped on the light. She was wearing blue jeans and sneakers and was glad she'd put her hair up in a bun.
When your heroine is about to go walking into danger, do you care what she's wearing? or how she's wearing her hair? I think not! You want to know what's in that basement! This information is relevant to the story, but it might come earlier on, or later, if she, say, falls and tears a hole in her new blue jeans when she trips going down the stairs. That's another way to "show" your readers what she's wearing without stopping the story to tell you.
While editing my own work, I keep these types of scenes in mind, how much time I take away from the plot, along with dozens of other silly mistakes that happen when you write a novel. Another thing I keep a sharp eye on is how often I repeat information. To the point where a reader will think, "oh yeah," or will they think, "I got it already, can you tell me something new?"
Details are important, but they should be interspersed seamlessly and they should advance the story, not take you on meandering detours that don't go anywhere. Stay on topic and keep the action moving!