By using fewer words to obtain the effect you desire, you will force yourself to use more accurate and powerful words. Communication is the primary job of the novelist. The kind of prose that most powerfully communicates ideas is simple and direct. You can't entertain a reader if he doesn't understand the story-line. You can't affect your reader emotionally if your prose is so dense it weighs him down.
Good prose contains vivid metaphors, similes, and striking images.
A novel would be flat and dull without them. But if you are using them every third sentence, or your similes are so involved it takes a whole page to present them, you are not communicating with your reader. There is an old example journalism teachers use about a city editor who once sent an inexperience cub reporter to cover the Johnstown Flood. After waiting hours and hours for the reporter's story to come over the wire, the editor was beginning to get very angry. Finally the teletype began to clatter, and the kid's story, ten thousand words long, began to print out.