Why should I research? It’s a fantasy novel, everything is made up anyway.
What should I research? There’s no such thing as hyper drives.
Research for writing isn’t just scientific, or library work. It is also important to research social structures, and people watch. Research lends an element of reality to your fiction, anchoring it into a solid idea that your readers can hang on to while they suspend disbelief about everything else fantastical going on in your setting.
For example, if your characters are riding horses and you don’t know the first thing about taking care of a horse, jumping on and off their horse like they’re driving a car, leaving it anywhere they please and expecting it not to have moved… Your lack of knowledge shows and any reader who has a basic understanding about horses will be offended and thrown out of the book.
Anyone who DOES know horses will put your book down in disgust. A horse is an animal with its own brain and motivations and not all horses are exactly the same. They will react to different stimulus different, some horses are shy, some are bold, some are extremely food motivated.
Same goes for cars. You know not to leave the keys in the ignition or to leave it unlocked on the side of a busy street. You know that you can’t drive on a flat tire. Your character doing all these things without acknowledging the consequences of them in your story will make people irritated at you, not your character for being dumb. If your plot depends on the character getting from point A in the city to point B in the city and they have to take a special mode of transportation, look into how that works.
This isn’t to say that you need to be an expert on everything horse-related in order to have horses be in your book for 0.5 seconds. However, having a basic understanding of what horses eat and how people take care of them would ground your fiction with enough realism that your readers will be able to forgive you the goat horns and bat wings on your main character.
If you are writing a historical fiction, look up fashion of that time period. Having women dressed for a different century than what you established in the narrative is a good indication that you don’t really care about the story or the reader enough to bother. If you haven’t researched your time period, its not really a historical fiction…
Are you writing space fantasy? Even if the technology doesn’t exist now, knowing what we currently have will give you an idea on how to explain the technology of the future. Maybe certain franchises didn’t explain how Warp Speed actually worked, but they did understand that stars are far apart and that fighting in space is a 3D affair. They kept a sense of reality in that there is some kind of work that must be done to maintain your equipment. You can still dramatize, but having that underpinning of reality will make the story hold up better in that second or third read.
Research doesn’t have to be a big involved thing either. It doesn’t have to be done at a library or on the internet. Personal experiences are a kind of research as well. If you don’t know how people work or understand them, its impossible to write believable characters. An example of this would be a white person trying to write people from a different culture. If you only know people from that culture as what you’ve seen on TV, you will end up with “Hello my name is Apu, welcome to Seven-Eleven.” The character would be nothing but stereotypes as viewed from a white perspective. This will alienate any readers who aren’t white. Not everyone who reads fiction is white. It is completely okay to write characters you don’t actually identify with or as, but make them people and not just cardboard cutouts by doing some research on how their culture influences them.
Further example is writing characters who are much older than the author. Adults can act childish from time to time, but to have all of them acting that way all the time is annoying to read. Adults grew up in different circumstances. When you don’t know that home computers didn’t become a thing until the late 1970’s and you have adults acting weird about logging into a computer, you’re missing a frustration that is universal. You weren’t born knowing how to write or read or drive a car. Imagine not learning those things until you’re in your twenties and being asked to do them without getting any instructions first. They don’t get computers because they were already adults when computers became a thing.
This extends to writing characters that aren’t the same gender or sexual orientation as you. Making them act stereotypical will offend your readers. Researching what events led to that character becoming who they are now will add a realistic depth that makes them not only more understandable but more likable, even if they’re the antagonist. Most importantly, this makes them more memorable.
Write what you know and when you don’t know it, go find out.