Phones are already using different formats for image storage. Apps are already sending those at different qualities and formats when you share them. You should

Phones are already using different formats for image storage. Apps are already sending those at different qualities and formats when you share them. You shouldn't just take an image from your phone as-is, stick it on a website, and display it at 400x400 or whatever. Firstly, that won't work if you took the image with an iPhone, since it uses HEIF, which isn't supported by any browser. Secondly, it'll be orders of magnitude too big. Sites will care about this stuff when it impacts their metrics like first-contentful-paint, which will soon begin impacting Google search ranking.