Writer vs. Storyteller

Worldbuilding can be a complicated and extensive hobby. But for many of us, we have a SMART Goal that we are aiming to accomplish. Many of us want to publish a novel, while others are Game Masters for our favorite tabletop RPG. For both of these, we need to approach worldbuilding differently.

Why Are These Different?

With writing, we as authors give our readers a Character to experience our world through. The reader takes no part in developing the world, except perhaps through feedback in early drafts. This makes it to we don't need to have every single thing planned and explained as we go. Writers don't need millinia of historical backstory and to know the names of thousands of minor characters.
In roleplaying games, however, GMs can not predict what their 3-8 players will want to do, and to force them only into what we plan is to risk an unsatisfying play experience.GMs need to make characters on the fly, and deal with surprising dice rolls killing major characters. Feedback is almost constant and expected.
Then how do we efficiently worldbuild for each of these situations?

Worldbuilding for Readers

The key point to remember about worldbuilding for a novel or other contained story, is that you only have one audience. One reader. Books are inherently solitary excursions into your world. What you write is what your reader will experience. This makes it easier to use your worldbuilding for personal reasons, such as to ensure coherency of your writing or for planning out chapters and plots. Better though, is to use your worldbuilding to create further insights into your world for readers who wish to dive deeper. This additional writing shouldn't subtract from your readers who partake in them, but also should be neccessary reading for those that only read your book.
It is key to always remember that you are writing for only one reader. Not hundreds. You are trying to pull one reader in for a few hours at a time. You are wanting them to want more and then to ask for more. Provide that by only worldbuilding to enhance, not to explain, not to fill your world.

Worldbuilding for Players

Players are fickle beings. They have their own lives, which they pull away from for hours at a time, as a group, to be apart of your world. Besides being a group activity, it also is not solely contained within the confines you as the GM may try to put on it. Mentioning one beggar boy on the street may take the party down a whole slew of quests and adventures seperate from the dark armies growing in the other direction. As a GM, you have to be prepared for players to go "off the rails" and take on their own lives.
Here, Worldbuilding is more about making sure you are ready to cover any aspect of your world. You do not, however, want to world sprawl into it. Begin using seasoning to open up options to your players, and backfill in the worldbuilding after your players have asked about it. This saves you time and headache, while also allowing your players to feel like they are truly discovering your world.