[afterthefact]

I think there is a fine balance. Of course, the better your vocabulary, the better you will be able to clearly express your thoughts. However, if you overuse big words, and do it only for the sake of using them when a more simple word would suffice, then it will not only come off as somewhat arrogant, but it will also alienate some, if not most, of your audience. It requires discernment to know what vocabulary they have, and are expected to have. Remember: having a limited vocabulary, to a certain degree, is not a sign of limited intelligence; most people have no need for big words, so they very well may have spent their time on learning things more pertinent to their needs and desires.