"One of the really bad things you can do to your writing is to dress up the vocabulary, looking for long words because you’re maybe a little bit ashamed of your short ones. This is like dressing up a household pet in evening clothes. The pet is embarrassed and the person who committed this act of premeditated cuteness should be even more embarrassed."
- Stephen King (On Writing: A Memoir of the Craft)
I couldn't agree more. Unless it is absolutely essential for you to write a word that most people would need a dictionary to understand, you're only dressing up your language. And by absolutely necessary, I mean, when there is no other word in the English language that conveys exactly what you're trying to convey.
If you're one of those people, who insert big words in their writing and convince themselves that those few words show what a wonderful writing style they have, allow me to tell you it that doesn't work that way. The only thing it does show, is how incredibly ordinary the rest of the writing is!
Don't use words like 'perspicuity' where a simple 'clarity' would suffice, and I won't call your language 'magniloquent' when I can just call it 'pretentious'.