“There are many plausible reasons that the use of million-dollar words would lead readers to believe that an author is smart. Intelligence and large vocabularies are positively correlated. Therefore, by displaying a large vocabulary, one may be providing cues that he or she is intelligent as well. Secondly, writers are assumed to be conforming to the Gricean maxim of manner, ‘avoid obscurity of expression’. If authors are believed to be writing as simply as possible, but a text is nonetheless complex, a reader might believe that the ideas expressed in that text are also complex, defying all attempts to simplify the language. Further, individuals forced to struggle through a complex text might experience dissonance if they believe that the ideas being conveyed are simple. Thus, individuals might be motivated to perceive a difficult text as being more worthwhile, thereby justifying the effort of processing. […]
Why might we believe that the experts might be correct in recommending simplicity in writing? One theory that predicts the effectiveness of straightforward writing is that of processing fluency. Simpler writing is easier to process, and studies have demonstrated that processing fluency is associated with a variety of positive dimensions. Fluency leads to higher judgements of truth, confidence, frequency, fame, and even liking. Furthermore, the effects of fluency are strongest when the fluency is discrepant — when the amount of experienced fluency is surprising. As such, it would not be surprising if the lower fluency of overly complex texts caused readers to have negative evaluations of those texts and the associated authors, especially if the complexity was unnecessary and thus surprising readers with the relative disfluency of the text.
Both the experts and prevailing wisdom present plausible views, but which (if either) is correct? The present paper provides an empirical investigation of the strategy of complexity, and finds such a strategy to be unsuccessful. Five studies demonstrate that the loss of fluency due to needless complexity in a text negatively impacts raters’ assessments of the text’s authors.”
From, and Read the study (PDF): http://www.psych.utoronto.ca/users/psy3001/files/simple%20writing.pdf