I'm a character oriented writer. As much as I would love to write something as plot oriented as the "Harry Potter" series or the "Pendragon" series, it's not meant to be. I love my characters too much. now, it's not a bad thing to be character oriented. I can't think of a single romance author that's more concerned with their plot than their characters (mind, they also have a formulaic plot 9 times out of 10). The top plot-oriented novels in the world have a much lower focus on inter-character relationships (as a rule).
Now, what in the world does this have to do with the world?
The world is your other character. It doesn't matter if you set it on modern-day Earth or not, you have to world-build everything to a "T" or have everything turn into a lawless, illogical blob (especially in fantasy). The world is normally seen as your background and nothing else, but just like our planet/universe, the world you create to write in changes. It has its own history and backstory. In any story without a god(dess) or god(desse)s, the world you write in is the closest thing to a deity you'll have. The world is the thing that develops your characters into what and who they are while you're writing.
Aside from all of that, a well-done world is fun to work with. If you define your world as an asteroid colony floating in space, for instance, you have to work out the gravity issues Do they just live in a low gravity atmosphere? Do they have a core of some hideously dense material that produces enough gravity to compensate? How about a machine that (somehow) produces an increased gravity field?
Now, just from this one little issue, no matter how you choose to solve the gravity thing, there are problems that can arise and enrich your plot, giving more credence and belief to your world. Following are some examples:
LOW GRAVITY LIVING: Now, if they never EVER leave the asteroid colony for anything larger, then they should be fine. However, consider this. If you SOMEHOW had your characters find an asteroid, say, the size of the moon, that would be one-sixth the gravity of Earth. As soon as they go to a higher-gravity place they'll be hugely weak because, unless they train specifically to deal with higher-gravity boides (which most won't), they'll be developed muscularaly to deal with that lower gravity. Not good news when they have to lift that forty-pound box and, instead, just drop it on the floor and shatter the tiles.
DENSE CORE: Now, once its there, the super-dense core works pretty danged brilliantly. The problem is getting it there. If you have people trying to harvest a small chunk of super-dense material, they would ahve to get it off of a large chunk of super-dense material or get lucky and find shrapnel. Then they have to get it to the core of the asteroid. Now, all of this has to happen without killing everyone involved. That would most likely involve some kind of anti-gravity device. One would think that they had a gravity producing device before the anti-gravity producing device, so why couldn't they just use that? You could also have a colission between the super-dense matter and the asteroid, but that's too unbelievable even for me. A super-dense asteroid raises a whole new slew of problems dealing with objects in orbit and, if whichever author makes a slip in their research, a space material far too dense to support most forms of life.
GRAVITY MACHINE: Now, this seems like it would make sense. It's just enough suspension of disbelief for people to go along with. We're talking science fiction, so I won't even question the practicality of making that much of an increase in gravity. This is an easily explainable option, but let's take a look at some other things. Producing so much gravity within an asteroid could pretty well start to collpase the asteroid (asteroids aren't exactly as structurally sound as a planet). Assuming thatthey reinforced the asteroid, what happens if the generator freaks out or fails? You could have too much gravity produced and, even with the reinforcement, crush the asteroid along with the people living on it. If it went in the other direction and completely shut down, people wouldn't know quite what to do. It's not as dangerous, but having that low gravity could provide a huge number of tiny problems in daily living (can you imagine what would happen to the mothers and fathers when their children figured out they could jump many, many feet at once?).
Now, it may not sound fun, I know, but I'm really not forbidding you from writing anything with any issues involved. If you look at your world as a character, issues are good. As long as, just like a character, you don't forget things when they become inconvenient. If your character has arachnophobia, you can't just make them handle a tarantula calmly because they need to for some reason. The same is true of your world. If the house your twenty-seven characters live in only has one bathroom, they can't all get up and do what they need to starting at six A.M. unless you move them outside of the bathroom. Sinks, garden hoses, shower schedules, swimming pools - anything could do.
Now, go out an world-build! Have fun with it! Make a giant earthworm in the center of your planet that comes to the surface whenever it rains! Imagine the fun you could have with that...