When writing a novel, language is important. You need to portray the right actions and emotions so that the reader understands what is going on. For that, you need accurate language.
Immersion is also important: it keeps the reader reading. Immersion is about keeping the reader focused on the events of the story, and not distracting them with unbelievable actions, unrealistic use of resources (I recently read a book in which the writer implies that a palace has been built of obsidian – a material wholly unsuitable for construction) or language.
If you don’t want your reader to think about the language you’re using, you need to use it well, in an unobtrusive manner. The best way to do this is to use the most efficient language. Efficiency in language is about conveying an idea accurately to the largest proportion of readers in the fewest words, using the shortest words available.