Less is more is a very important design principle. It is as important as the 80:20 principle. It means that which is less complicated is often better understood and more appreciated than what is more complicated; simplicity is preferable to complexity; brevity in communication is more effective than verbosity.
Next we will use an animated image to describe what is less is more.
The popularity of flat design in web application design also proves the importance of less is more. Many famous companies adopt flat design in their products such as Microsoft's Windows Phone and the new Google logo.
Note : image is from @Ray
