A common situation, at least for me, with web graphics is you’ll get an image that needs transparency but due to file size constaints or browser compatibility has to be an 8-bit png.
These images undoubtedly will contain far more than 256 colours, so some form of dithering would be required to make them more visually acceptable. The problem is images with mixed content. Text looks best with ‘no dither’, photographic images almost always with ‘diffusion’ and in many cases gradients with a ‘pattern dither’. Photoshop one allows you to choose one, so which area do you sacrifice?