Whenever I read a book, a story or a poem, I am aware of the infringement of reality upon the narrative. Verisimilitude comes from the recognizable; I like Walter Mosley's books because I've lived in some of the areas his stories take place. I recognize places his characters stop at or pass along the way. It makes his stories more realistic to me. I like Charles de Lint's work because I recognize the mythical stories he bases his characters on - so when he invokes Raven or the Crow Girls, or Coyote Woman, I find resonance within the cultural realities. I try to do the same with my writing.
That leads me to research before, during and after the process of getting that first draft down on paper (even if it is electronic metaphorical paper). So as I write I check things out. Where did the people I'm mentioning live? Were they mostly in one specific neighborhood? Where did the more affluent members of that community live, the poor? What kind of transportation could they afford, what was their most common dress, how did their hair look? The one hundred plus questions that come-up as I write must have reasonable, defensible answers.
That leads to the pursuit of information that will never be used in my story; what are the common family names of this community, what do those names mean, what does that say about where they came from in the old country, how was their language different, etc., etc., etc. Do I need all of it? Probably not. Do I like reading it? Definitely. Does it take too much time? Absolutely.
Besides, who knows when it might come-up in a game of trivia?