"Anything that makes a text hard to read and understand, such as unnecessarily long words or complicated fonts, will lower readers' evaluations of the text and its author... The continuing popularity amongst students of using big words and attractive font styles may be due to the fact that they may not realize these techniques could backfire...."
Okay, but there's one big problem: If you make it really clear, people can see what you're saying, and if the substance is bad, you'll be caught. Which is great. Even better: In the process of making yourself clear, you may see what's bad and fix it, or — simplicity par excellence — refrain from publishing anything. That doesn't work for students who must hand something in, but it's professors who really annoy me.