For my book Doctor Dead, which is set in 1904, I did a lot of historical research, or as my wife calls it, “wasting time reading ancient newspapers instead of writing.” I thought it was important to get the details right. This is not so much because there were likely to be many readers who would be able to correct me as regards, say, the top speed of a Welch motorcar with the new hemi engine, though certainly I wouldn’t want to be embarrassed in that regard. More so, it’s because reading the publications of the time and place you’re setting your story in, gives you a feel for the language and attitudes, current events, and every other little detail that helps a reader feel that they’re really in an unfamiliar but real setting. It’s hard to write the story first, then add that stuff afterwards, because you often don’t have any idea what specific crazy things were going on at the time that you have no idea about. How do you look up something you had no idea ever existed?
Not a lot of these details end up in the narrative; you don’t know what you’ll need until you need it. But having them already floating around in my head, I find, lets me be specific when I have an opportunity to make things real — that a light switch is a button, for instance, rather than the generic switch I’d be tempted to use if I hadn’t seen a picture of the real thing in Popular Mechanics June 1903 issue.
Of course, you’re not going to find every detail you need in advance, but you can always put in little notes in, like [light switch] to remind you to do the research later. I did a lot of that too, like when I wanted my characters to go out for lunch and didn’t know whether they could plausibly have had [burgers and cokes?]. So I flagged it for later. I absolutely didn’t stop right there and spend two hours reading about the 1903 World’s Fair, where the hamburger was introduced, and looking up which cities had Coca-Cola bottling plants at the time. No, I did not. Shut up.
Plus, knowing about these things in advance means they can also become plot points rather than just set dressing. If you already know that your character whose hobby is photography, would have read an article about radium that you spotted in a photography magazine of the time, that can give you the idea of introducing radium into the story, knowing he, unlike the other characters, would suspect it was a bad thing to ingest, because the article described it as causing burns when carried in a vial in one’s pocket.
And finally, knowing these trivial details can help you in real life. For instance, I was at Caribou Coffee today and their trivia question was, what year was root beer invented. I knew that. Saved 10 cents, which in 1904 money is enough to buy two root beers. Payoff!