I think this is not news if you’ve studied something like design. Hopefully you learned something about the principles of typography. They’re the same for both the web and print. It’s easier for people to read a text that isn’t justified.
If a line of text is forced to fit the given space, some words will have more whitespace in between than usual. That may be hard to read for people with visual or cognitive impairments. On the other hand, words can be bunched up together. This will make reading difficult, too. The reader might not be able to make out where one word ends and the next starts. Just let the text flow ...
It is easier to read a text that is not justified. Imagine long words. They will increase the whitespace between the words and it makes it hard to go to the next line in the paragraph.
