If you want your buildings, even sci-fi buildings, to look real, keep construction concepts and physics in mind. If a model looks like it’d fall apart in real scale, don’t be shy about adding a support or an I-beam here or there. As long as the supports don’t interfere with game-play, so ahead and be a construction snob.
Personally, I’ll decide whether to use a butt joint or a mitered corner on a model just like I’d decide which to use if I was putting it in my house. But I’m insane 🙂