They say in photography "anything that doesn't add to the picture takes away from the picture".
Basically this means simplify where possible, and applies to more than just photography.
Discussion
Orwell says the same about writing, these were his six rules:
1. Never use a metaphor, simile, or other figure of speech which you are used to seeing in print.
2. Never use a long word where a short one will do.
3. If it is possible to cut a word out, always cut it out.
4. Never use the passive where you can use the active.
5. Never use a foreign phrase, a scientific word, or a jargon word if you can think of an everyday English equivalent.
6. Break any of these rules rather than say anything outright barbarous.
I like those rules :)