I had the same thoughts. You may be able to reduce bandwidth if you're doing something like responsive images (even then, over a mobile connection, I'd rather low-res images be sent to phone despite the pixel density of my screen), but at the expense of taking longer to start rendering. There's probably a sweet spot between time to render and page weight, but I think this probably makes things worse. I'd rather see things load slowly than double parse the document and see nothing but a blank web page (which i might interpret as the site being completely unresponsive).

Perceived load time is often as important as actual load time. A site that takes 10 seconds to load but spend 80% of that is showing a white screen may feel slower than a website that takes 15 seconds to load but only 10% of the time is white screen.