[MengerSponge]

I doubt there were deep studies, because there so much of a document's design is a matter of taste. For example, Don Knuth really liked a certain generation of math journals, so he built TeX and CM to emulate that. Just because it's the default doesn't mean it's an optimal design.

I'm partial to serif fonts, and Scala in particular, but Apple's design documents are beautiful too, and I can't begrudge someone wanting to emulate their design.