Never...

From the famous George Orwell's excellent essay Politics and the English Language, written in 1946. Much of it is still relevant today:

Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.

Never use a long word where a short one will do.

If it is possible to cut a word out, always cut it out.

Never use the passive where you can use the active.

Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.

Break any of these rules sooner than say anything outright barbarous.

Courtesy: http://jeremy.zawodny.com/blog/