I have done in the past, I used to be quite a big fan of fantasy novels and such, I have quite a few series of books and though we are trying to get rid of stuff out of the house I can't bare to part with them ^_^
That enjoyment of them has led me to writing up ideas if you like for my own fantasy novels, that has included world building, character creation and such. It tend's to be that when I write (or type) something the words tend to flow, even now when I type this I don't really know what I am going to write until I do it! But yeah it was always the way when I used to write in that I never sat down and came up with ideas in the sense, ah I want 7 houses and they are at war and there are these alliances, I would write like I was following a group i.e. akin to the lord of the rings stories or the Eragon books so I would be creating and experiencing the adventure / world as a someone wholly new to it would experience it. Whether that translates to good creative writing or not I have no idea!
I think my issue with keeping it going and actually creating a full length novel has always been time and that has only become much more reduced with little un's. It is one of those things I have always wanted to do is release a novel, I know Elliot's book is an entirely different category but I do have some respect to him for making it happen. I have never really had the confidence to go out and explore how to make something like that happen.
That said James, if you are starting to get into it now, I know DnD dungeon masters benefit from creative writing in that being able to come up with their own scenarios and such, hint hint 😉