Choose to use a word, not because it is short or long, but because it serves your purpose.
From Beginnings of Rhetoric and Composition, by Adams Hill:
Advantages of Short Words
Short words save time for both writer and reader, not only because they are short, but also because they diminish the amount of effort required to get at the meaning: they are, as a rule, the familiar names of familiar things or of familiar ideas; they belong less to literary language than to living speech.
Advantages of Long Words
Long words are needed for the treatment of many subjects that are remote from ordinary events and simple feelings; and they are needed more and more as the conditions of civilization become more complex.
One long word is sometimes shorter than an equivalent phrase made up of short words, not only because it may have fewer syllables, but also because its meaning may be caught before the whole word is pronounced. "Constitute," for example, is shorter than go to make up, "inaugurate" than invest with a new office by solemn rites, "innumerable" than too many to be counted.
In stately compositions in which sound and cadence count for much, long words play an important part, — in the works of Sir Thomas Browne, for example, of Jeremy Taylor, of Dr. Johnson, of Gibbon, of De Quincey, and in the early writings of Ruskin and Macaulay. They are more frequent in Milton than in Chaucer, in Addison's "Vision of Mirza" than in his paper on fans, in Irving's "Westminster Abbey" than in his "John Bull," in Tennyson's "In Memoriam" than in his ballad "The Revenge," in Bryant's "Thanatopsis" than in his "To a Waterfowl."
Big Words for Big Words' Sake
A writer who uses long words in order to give an air of magnificence to the petty or the mean is in danger of obscuring what might otherwise be clear, of sacrificing sense to sound, of degrading noble language to ignoble ends, or of gratifying a wish to be "funny."
"The grandiloquent man," says George Eliot, "is never bent on saying what he feels or what he sees, but on producing a certain effect on his audience."
The American Romantic poet James Russell Lowell gives examples of what he considers overwriting:
The object of writing is to convey information clearly and quickly.
Choose the words best adapted to the purpose in hand.