Other than bigger worlds needing more work, size alone should not be a concern for world-builders. A world can be as small or as large as you like. The only really important thing about size is that it is the right one for the job.
As I mentioned last week, thinking of world building as two things and not one may help you avoid unnecessary or wasted work; so too may thinking about the scope of your world in the early stages of your project. Too large a scope and you’ve wasted your time developing a load of details that will never impact an end product. Too small and you’re going to be backtracking frequently to fill in the gaps, breaking the flow of your later work. Some of this back and forth is almost inevitable as the creative process never stands still and things evolve. However, better to minimise the waste if possible.
This means that I include a very broad selection of possibilities in my definition of world-building, and not just complete continents or whole planets full of imaginary cultures (though these are impressive). Indeed, at its smallest, a world for a specific project could be very small indeed.
For example, adverts often present the real world with some strange twist that sells the product: talking meerkats, singing neighbours, animated breakfast cereal. You get the idea. In each of these instances, there is world-building. It is not the real world you are looking at; it is a fictional variant of one. If you really saw some talking meerkats or your cornflakes struck up a conversation over the breakfast table, I doubt that you’d have the inane grins and cheers that our advertising families do. These worlds may be very similar to ours, but they’re not the same, and someone had to create that difference, just like any other fictional world.
If you think that advertising is a little crass for the noble art of world-building, consider the short story, or even flash fiction. These bijou efforts can be extremely short, and yet the fictional worlds they present still need to conform to the ideals of good world-building for the whole thing to function at its best. Sloppy and inconsistent work at the world-building level leads to a substandard end product regardless of size.
In fact, presenting a world in a small format can be more challenging that one where you have room to develop ideas at length. As an exercise, try defining a new world with only 3 sentences to give the reader clues. How much can you cram in? Can you get across the sense of a different place?
Also, have a look at some adverts and try to work out what they’ve done to define their variant reality. Can you use any of these tricks to explain your own?