If you implement lazy image loading yourself in JS you will see that the implementation actually makes a big difference in how noticeable it is. The browser does a good job with it. Of course your internet connection can limit you, but it just won't do so on regular broadband connections for sound image sizes.

You can always construct a theoretical case where it does not work great. But on those pages and connections loading all the images in advance will usually also lead to a bad experience.