Big words compress information. However, they are also more difficult to understand -- they are used more rarely, so they are more likely to be forgotten, or may take longer to recall. I feel like the tradeoff rarely favors using a big word if the goal is conveying information.
I feel like this same tradeoff comes up in math. After thinking about a problem for a while, the solution can be compressed into a short equation. However, presenting that equation alone presents a very challenging task to the reader to try to unravel the meaning of the equation (especially if it has lots of greek symbols, and the reader is not greek). I think it is often better to walk the reader through the key ideas that led to the equation.
Naturally there is a tradeoff. Sometimes big words and equations are good.
But I feel like they are often abused in order to make an author look smart, or even to hide a bad explanation by making it difficult for people to understand, and hoping that people won't ask questions for fear of feeling stupid for not understanding it.
I think explanations are like user interfaces. If the explanation fails, it is probably the fault of the person doing the explaining, NOT the person listening.