Ancient history: when I wrote BCPL roff, I immediately noticed the page-level density gradient from thick on the left to thin on the right if padding spaces were inserted from the right. I next tried randomly distributing the padding. This was even worse because it led one to perceive false phrase boundaries at the wider spaces. The text became maddening to read. Only then did I try alternating left- and right-padding, which has stood the test of time.
But all this is a frill. Justified text seemed like a nice idea at the time, because it distinguished computer-composed documents from old-fashioned typewritten documents. But it soon became old hat and people migrated back to ragged right margins, which may not look as neat from afar, but also seem to be easier to read both because of even spacing and because the variable margin provides distinguishablility to help a reader track vertical position on the page. Doug
