Can you provide sources? I’m curious. Borders are everywhere from lane marks on the roads to art frames. I tried searching for sources on Google with no luck.

> Unnecessary borders create visual complexity that increases the load on perception, which reduces cognition

That's difficult to believe in if you remove the word "unnecessary". Logical grouping of similar components in a UI using a border can only help group them. The framework for grid-based design was laid out by Josef Muller-Brockmann and heavily influenced the swiss/intl design language.

You now need to define what constitutes "unnecessary" :) otherwise its talking past each other.