“We need the tonic of wildness…at the same time that we are earnest to explore and learn all things.”
— Henry David Thoreau
Probably following the arc of expanding power in many zero-to-hero role-playing systems, most GMs have said the scope of their adventuring world grows as a campaign continues. This is commonly called ‘bottom-up’ design, where you start small and build up as the players explore further and expand their knowledge.
This is probably the most time-effective way to go about it. There’s only limited value in detailing the lands and cultures of the reptilian swamp satraps when the players’ immediately set off for the mountains. This also lets you react to your player’s individual interests and gives them input into the shape and color of the world.