You mean less than GUI resolution. And actually, while it is useful for <GUI resolution, there are other uses too. If, for example, you have a video that is 2560x1440, without the whitelist active it will be downscaled to 1080p, with consequent loss of detail; with a whitelist it will be upscaled to 4K instead. The whitelist also enables resolution-switching on the fly, and there are a few other situations where it’s useful.
May I recommend my whitelist guide…?
Plus, the issue of what happens when you play a 1080i/50 VC-1 clip at 50Hz with deinterlacing set to Off is still a problem even with the whitelist disabled, so that’s not a panacea.
I usually watch SD at less than full screen. 576p 4:3, for example, I watch as 1536x1152 (on a 65" 4K screen). It looks much clearer and sharper that way.
Yes, indeed, that’s true on most setups.