Does it make the text harder to read? A nice side effect of justifying text is that it makes easier to determine when a paragraph ends (or a line break occurs),

Does it make the text harder to read? A nice side effect of justifying text is that it makes easier to determine when a paragraph ends (or a line break occurs), especially if there's no vertical spacing between paragraphs. But justification needs to be paired with word breaks, otherwise lines with long words will look unnatural. Most (all?) books I have at home follow these two rules, and if they didn't they would look amateurish to me. Of course the web is a different beast, but if the line length is reasonable, I think the same rules can apply.