This is absolutely it for me. It's also why I like paragraphs to have some level of spacing between them.
I'm currently reading a book that has quite minimal indentation on the first line of a paragraph, no spacing between, small font, and justified text. Every page is just a wall of text. It makes it noticeably more tiring to read than others that I've read recently. It seems to be a trend in more serious historical tomes. The last one I read, the Beauty and the Terror, was similarly typeset.
It's one of the reasons I like reading on my kindle.
And lowercase letters are easier to read than ALL CAPITALIZED LETTERS IN A HORIZONTAL LINE OF TEXT.
Justified text is the same thing, but vertically. Your eye reaches the end of the line, and the next one is likely slightly longer or shorter, so it is easier for your eyes to find the next line instead of reading the same line over again, and also easier to see the whole shape of a particular paragraph you want to refer to later.
I do like well-hyphenated justified paragraphs in print, that also let you fit more words per page. But even there, I prefer the organic, non-uniform look of ragged text.
