Doesn't that depend on how good the implementation is? Some modern TVs and receivers have exceptionally good scaling built-in. I'd also bet with certain types

Doesn't that depend on how good the implementation is? Some modern TVs and receivers have exceptionally good scaling built-in. I'd also bet with certain types of displays (eg: OLED, HDR and/or local dimming) there's benefits when there's a different aspect ratio (eg 21:9), letting the TV do something different to the backlight when it knows there there is no content in parts of the display vs getting a black signal.