So a small image quality test for different values of jpeg:sampling-factor in ImageMagick.
Original image - Hakamada Test. Image size is 836 Kb.
Used php-imagick extension. The image was opened, jpeg: sampling-factor was set and the image was saved with 50% quality.
The results, in comparison, indicates the sampling factor, size of the image. Shown single fragment of the image (color distortion):
As you can see, the difference between 4:1:0 and 4:4:4 is as huge as 31KB (it's only 3.7% relative to the size of the original image).
Therefore, is it so important to win so little in size and lose so much in quality as it is?