People world build in one of two ways: they either start from the small, mundane things and work their way to larger ones, or they start from the creation of the world, and finally come down to earth.
World building can be seen as a funnel, with the epic ‘and the land was parted from the waters’ at the large end and the ordinary ‘the decor the privy’ at the spout.
You need to know how your world was created, or at the very least, some idea of who your characters think the world was created. This helps to understand why your characters think about the world in the way they do, on a collective consciousness level. Was the world created violently or in a loving and peaceful manner? What effect does this belief have on the way the people, as a whole, live in the world you’re building?
But you also need to know the decor of the privy. Well, not this exactly (but maybe, depending on the story), but knowing how the toilet is decorated says a great deal about the character and the world in which they live. What kind of toilet is it? Why is it that way? Is there any decoration in it? Why or why not?
Knowledge of both of these things is essential. It makes your world a real place, filled with real people, doing things for real reasons. Either way is appropriate. But both ways must serve the story.