When you build a new world, how careful are you about historical accuracy, and/or the culture a particular idea comes from? As a reader, do you get angry when an idea from Ming Dynasty China is tossed into a world that has Rennisance Italian whatevers? As a reader, how much attention do you pay to this sort of thing?
It depends on what the book is doing.
If the story is mostly psychological or allegorical, I don't mind if the world exists primarily to support that story.
If you're going to do something where the world is an attraction, there have to be reasons in place for why and how things work. How much of that is in the book is debatable, though what's there should be consistent and what can be deduced from it should make sense, but have it hang together.
Readers may have specialist knowledge in a lot of different fields. My own formal academic background is in molecular biology, and I am very unlikely to be tolerant of gross stupidity for a mol bio plot element. I don't think getting enough in to satisfy the specialist does any harm for people who don't notice, and it makes it a much more enjoyable read for people who do. If your quasi-medieval fantasy world has magical healing, for example, think through what that does to infant mortality rates compared to a real medieval setting, and have some explanation in place for why you haven't had a disastrous population explosion.
The other thing that particularly irks me is random suns of different colours; because if your universe works on the same basic physics as ours, only stars of certain sizes will be blue-white, for example, and that has implications about how close in a planet can be and still be habitable, and how long its year-length will be and so on. The maths there is quite straightforward, so look it up and get it right. And if it
doesn't work on the same basic physics as ours, you'd better have the implications of that thought through, particularly if you want to have people in it.
