Handsome module... images begin to charge as all the rest is already displayed on the site.
Do not forget to install the third party library.
Let us first look at the performance without this module. I have a multiple image field where I introduced fairly large files. (There are sites on the net that can measure the performance of your site.)
Here you can see that it takes (with all the large files), 2.469 seconds to load the page.
You'll see images play a big role.
After installing the module, you can choose to display your image field LazyLoad (note: apparently only for responsive images!)
With this setting active, you now see that the page loads in 0.776 seconds.
You'll see that images load, after the content (text and other images that are not lazy load) is shown. This module is an asset to show large amounts of pictures.