images loading on scroll experience

Traditionally I have created sites where the images all download at once, but you often see sites where the images only download once they are scrolled to and in view in the screen. I presumed this was solely increase download speed. In my experience it makes very little difference in actual download speed, as the site downloads the images download asynchronous in order of the page.

I am not referring to pagination downloading on scroll (infinite scrolling), simply images downloading when they are in view.

But what about actual user experience? Do you think it's a better for visitors to see the images download, as perhaps it makes the page feel more dynamic or alive for them, in that although the page is downloaded, its still active to them. Rather than just a page that has downloaded fully and is essentially dead?