Yeah, they don't look great with a ragged right edge. With justified text the structure would be far clearer.
Such things are not required in digital media where each reader might have completely different spaces for text to render within. And, ideally, the content and its formatting are structured in such a way as to allow the user to apply their own formatting if desired.
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Then along came Microsoft Word, which inserted vertical space between paragraphs instead. Now most people think it's supposed to be that way.
I have no citation for this, but have noticed that novels in print use indentation rather than spacing.
the earlier tradition was that you'd add a pilcrow or some other distinctive mark at the start of a logical paragraph mid-line so that as little paper (which was either baby cow parchment or made of precious linen) was wasted on whitespace. For an example, look at a 42 line bible [2] or eric gill's book on typography [3].
[1]: http://www.thenewgraphic.com/2012/06/jan-tschichold-penguin-... [2]: http://www.hrc.utexas.edu/exhibitions/permanent/gutenbergbib... [3]: http://www.olivertomas.com/books/eric-gills-an-essay-on-typo...