[nine_k]

Reiterating and showing from different angles and in various contexts = good.

Not getting to the point, or giving relevant context and precursor ideas, while dwelling on unrelated subjects = fluff.

I like my non-fiction the way I like science articles: starting with a summary, and diving into all necessary details later.

[readcarefully]

Technical writing must be this way.

However using poetic language in writing that's trying to communicate scientific understanding to everyone, I find, is useful and appropriate. Look at Carl Sagan's popular writings, or some of Asimov's more science related works for good examples.