Depends on the scope of the campaign I want. Overall, I believe in "small and useful" vs. "large that I won't use"

I don't need more than one city in a Cyberpunk or Urban Fantasy game.

Traveller runs fine with a single solar system. AKA, no jump drives. Even with jump drives, a dozen systems will do a campaign just fine for years.

My OD&D campaign has yet to have any travel beyond a week's journey from the main port city. I've run 20+ sessions and there is so much to see & do close by that even though the "larger world" is known to the PCs, they are so invested in the local area and its conflicts that they haven't even gone deep in any cardinal direction.

My Mazes & Minotaurs campaign is an island hopper through a misty archipeligo. I plotted 18 isles and after 20+ sessions, I think I've used 8 of them.

Regional. I started the latest world in the central region of a land mass, and have been developing different parts of it as I go. The previous group fleshed out much of the central region, while the newest group is located east. There's still a great deal of land unexplored west and north that, I guess, become the backdrop for the next campaign.:-)

That said, I think I could've continued running in the central location for a very long time, given the shifting political alliances, and places still wild and unknown there.

Start small and expand only at need.

Good rule of thumb, IME: slower pace, smaller scale; faster pace, further scale.

That way you are matching pacing, as that affects relationship development. It matches closer to life, from my globetrotting experience, too. It also helps you decide how much preparatory work you want to invest into the materials.

Fast and furious can easily enjoy a grand tour because it is all transitory. It is a survey course, a tasting not savoring, of the material. Conversely slow and subtle can easily linger around a single point because all pieces eventually impart textured meaning to the whole. It is (and I hate the potential elitist misinterpretation, but roll with the analogy parallelism with me) an upper division course, a marrow sucking savoring, of the material's multifaceted nature.

It's an axiom to support my GM laziness and lowered expectations. This is just happy fun time in imagination land for most of us, so I'll take the least resistance when I can. If and when I get more stellar players down for it, we can try more complex, experimental stuff. Until then, baby steps.