One always has a choice of words. Ergo, the use of specific words by an author must be considered a choice.
So, what would cause us to choose one word over another?
All words have denotations - that's what they mean. Their denotation is the relatively neutral meaning that you'll find in the dictionary when you look them up.
And yet...
All words also have connotations. That's what they mean. Or rather, that's the feeling we get from them. These connotations come from everywhere - from the physical sound of the word, to the emotions or cultural associations we've applied to them.
For example, we all want to be young and youthful, but who wants to be thought of as childish or juvenile?
These little contrasts are what make a house a home. They make [the difficult] [a challenge], and stretch quite far - consider the difference between smooth and polished. Good authors keep vocabularies of a great many words, and choose their words very carefully. When we read, we should pay attention to the words which the author has chosen, especially when we know they could have easily chosen another for the same denotative purpose.
The Eyes Have It, albeit a work of fiction, provides a humorous example that is too interesting not to mention here. Read it to see what fun an author can have, simply by exploiting the differences between connotative and denotative diction.