Most fictional worlds are not whole worlds. There has to be the sense of a world around your characters, obviously, but that does not mean that every area of your world gets an equal amount of attention. It may seem like a very basic point to make, but the area immediately around your characters is more important than the rest of the world. Take something set in the modern day in a small village in the Home Counties (because I want to make the point that world building isn’t just a fantasy thing). We know that Wales, Germany and Denmark are out there somewhere, and it probably contributes something to our understanding of the world to know that, but they won’t be detailed in the work.
Generally, your actual world, in terms of the space that shows up in the text, will consist of one of two things. Either it will be a single broad location (a city, a village, a room that people wander in and out of in extreme cases or plays) or it will be a line of such locations arranged to make a journey. You will never have heroes visiting every location in the entire real world, because you don’t have that many pages, and because that wouldn’t make for much of a story.
What that means is that you actually have different categories of places to define in constructing your world:
Places that will actually show up in the story- if you’re going to set something there, then it needs to be fully detailed, whatever ‘fully detailed’ means for you. Your level of description won’t be the same as mine, or anyone else’s, but in general, these are the places you need to know most about. Setting a fight in a bar? Then you should at least know the layout, not to mention whether there are any handy chandeliers to swing on. And possibly whether the landlord has decent insurance, what kind of patrons it attracts…
Places the heroes know well- these are places that they won’t actually go, but to which they have probably been, because they know them, and will refer to them, remember them, etc. You need to know enough about them to make those memories real, but probably not so many of the physical details. It’s about tone. Actually, that’s true of everywhere, but particularly so here.
Background places- these are places they’ve heard of, places things come from, or people, or ideas. They’re the place that war is happening in somewhere else, or where that magical sword must have come from, or where their cousin’s brother went to get a job in cabbage packaging. You need to know far less about these, because people know far less about far off places than they often think.