No matter of you’re writing a fantasy or a contemporary there should always be some form of world building. However, the questions you’ll ask yourself might differ depending on your genre.
Are your characters fighting aliens on a foreign planet? What’s the planet like? Who’s in charge? How’s the weather? What have the potential to kill them and what have the potential to save them?
Maybe you’re writing a contemporary YA. What’s the school like? Big, small, old new? Are they living in a small town or a big city? What’s their home situation like?
There might be more things to figure out in a fantasy. Such as if there’s magic, what’s the magic system like? What kind of governmental system do they have- kingdom, dictatorship, democracy? Do they have a military? If so, who’s in the military?
Even if I am a pantser I usually have a few things decided before I start writing. I usually know where the story takes place. If it’s in a existing place or if it’s in a made up town. Even if it’s a made up place I ruffly choose a place on the map so I have a few pointers on climate and the surrounding. So far I haven’t set a story on a far away planet but you’ll never know what the future have in store.
Considering I still haven’t chosen a story my world building is nonexistent so far. But I can happily say I’ve narrowed down the options from 6 to 5. I call that progress.