I'm not sure either way, would you say this makes it easier to read and I should make it the default?
How much of it is convention vs based in measurable outcomes is up for debate (maybe), but at least that’s where most every formally trained designer/visual artist in the west comes from.
On displays, readability works out differently, and that's why I speculate this has changed. For example, printed media uses serif fonts to aid readability, but on displays, sans-serif works better, especially on lower resolutions.
What? I'm pretty sure that if I pick any book in my shelf, it's going to be justified.
> Most web media are narrow-column format, so tend to be fully justified.
What #2? 99% of web media is ragged-right, the biggest reason being that it's the default, and that browsers have terrible line-wrapping and historically had no support for hyphenation. And justified text gets worse the shorter the lines are, because there are fewer options on where to insert newlines, leading to large spaces between words. Also, good justification requires fine-grained word spacing control, which doesn't work well with traditional low-resolution displays.
My MSc thesis advisor recently told that apparently thesis documents should be submitted with ragged-right lines these days because it makes them easier to read for dyslexics; while it makes sense, it must be a quite new guideline.