There's lots of things that are proven help type be more legible - good size, good line spacing, line width just right, good contrast, etc.
But then there's this idea of Vertical Rhythm - that all vertical units on your page should also fit within a grid. Is there any proof that this actually makes designs better, compared to just good spacing and structure? Could it be noticed in a blind test, does it actually provide an intangible nicety for viewers? Or is it just BS like the golden ratio?
I tried searching google scholar but couldn't find anything - any ideas?