Calibrated display has more NATURAL image and more pleasing to watch.
Uncalibrated display or bad setting may "tax" your vision a bit, how?

Our vision is auto calibrated by the brain minimising color error, white, so things looks natural.
Our vision is more of a relative, not really with fixed parameters.
Remember the red-cyan glasses for 3d? After using it for 15 minutes, our brain will re-calibrate (error correction) for the left and right color vision, when you remove the glasses try using the left eye only then the right eye only. You'll notice the eye which on cyan glass image will look more red-ish and where the red glass is you vision is more blu-ish.
Another example, if you use COOL white setting, your ceiling florescent lamp looks yellowish, its the error correction in effect, the brain accepts what you watch most as the referrence and accepts it as TRUE. When you switch to WARM then the florescent looks much natural and has more white to it. Why? Our eyes is being used to 6500K white from the sun. Even most of our florescent is also 6500k. Some low quality white leds are 9300k tho, they appear bluish, but not to worry all display has fixed this via factory level calibration, by compensating lesser blue into RGB for white.
This post has been edited by Mea Culpa: Nov 9 2014, 01:37 AM