Some people hate world-building and others love it. I consider myself to be the latter. When I begin writing a new story, the first thing I like to do is create the world.

A great way to think about it is like this. A theatre performance would be pretty boring without the set, backdrop, and props to great a spectacle on the stage.

It is the same with writing fantasy and science fiction (for me, at least). A story and its characters are made better by the captivating world around them.