Sally Kerrigan, for A List Apart:
You want to be a friend to your readers here, in the sense that you want to respect their time and attention. Except in rare literary circles, there’s no good reason to make your readers work hard just to understand what you’re trying to say. Each supporting argument or illustrative example you include needs to connect clearly back to your main point; the whole thing is moot if your readers trail off before getting to the cat food.
If you’ve ever attended college or university, you’ll know about a certain brand of opaque writing that’s a pain in the ass to read. It’s a kind of academic speak, which is often unnecessary, and potentially destructive: overly-complex phrasing can create only a surface impression of intellect. While there will always be a place for jargon, an expert in a field should be able to use relatively plain language to explain things to a layperson.
That’s not to say that you can’t or shouldn’t make use of esoteric vocabulary or complex phrasing, but clarity should take precedence.