Highliting everything highlites nothing.
This one is a little pet peeve of mine. I thought of two ways this piece of wisdom is true. One, if you are trying to highlite (with a real yellow highliter) the main idea of a passage perhaps for school or bible study, highliting whole sentences (paragraphs even!) accomplishes little. What you are highliting doesn't stand out at all. Not really.
However, by highliting just a few words here and there, key words that will bring to mind the main idea of a passage, you are accomplishing much. Plus, you won't go through so many highliters.
Another example of this comes from my job. We leave notes in a spiral notebook for the next shift. There are days when I come in that the entire page of notes is highlited. It is actually a distraction more than an assistance. It would be better to highlite nothing at all.
Two, sometimes the use of many words, being verbose (for all you SATers), is less effective than coming straight to the point. Granted, there are times when description is warranted, perhaps even a lot of description. But, just being descriptive just for the sake of description is just ... stupid.
For example, it would be better to describe something effectively in one paragraph than taking page after page to do the same thing. Obviously, I don't like a lot of description. But, if you read two versions of the same thing, and the shorter one gave you the same basic mental image, which would you have preferred?
Personally, I would prefer the one that highlites a few things, not everything.
P.S. - Sorry for being so verbose! ;-)