Receptionist? I think you mean "care navigator"

The problem is that in self-emissive displays like OLED the display gets hotter if more of the panel is illuminated, so to protect the panel from overheating the maximum brightness of the panel reduces as more of the screen is illuminated. So when showing a full-screen white rectangle the max brightness is lower than when showing a small rectangle. Some panels have a heatsink to minimise this, others do not, so the effect will vary from one model to another. This makes it very difficult to compare results, hence the standard window sizes. Movies very rarely show a full-screen white image, highlights usually only occupy a small part of the screen. The tests could include a range of window sizes, but if the sizes are standardised the manufacturers could still cheat.

Tencent can (and regularly do) censor wechat messages, which means they can see the messages, so there is no privacy. Although they usually only censor messages posted by Chinese users, they can read all messages posted anywhere in the world. No thanks.