I use this daily when building websites to get a feel for what a color will look like when it covers the whole screen, which makes it perfect for presentation slides as well.

做网站的时候，我每天都用它来为颜色选用找感觉，包括它看起来会如何、如果覆盖整个屏幕效果会怎样、做幻灯片用哪个颜色好等等。

youdao

Example of Vignetting. Notice how the screen corners get darker and more blurred and also show color separation.

渐晕特效例子。注意屏幕的边角区域是如何变暗、模糊和颜色分离的。

youdao

We're told that it will most likely be used on the back of color phones, much like the YotaPhone, but partners are welcome to get crazy on the front screen as well.

ENGADGET: E Ink reference phone and flexible display hands-ons (video)