Fade in in scroll will always be slower than the reading speed of a significant percentage of population.
This becomes worse for people who just skim content, re-read the text, or want to quickly scroll to a specific place in text
It can speed up the loading of the above-the-fold content because the images on the rest of the page can be loaded as the user scrolls closer to them.
It can speed up the loading of the above-the-fold content because the images on the rest of the page can be loaded as the user scrolls closer to them.