I agree with Rob Wierzbowski
Yes, the initial reason for using ems/rems was for *accessibility*, but we’ve since learned that it’s a great way to reduce the amount of messy, moving parts while discussing, designing, and developing layouts.
In practice, using rems has an added benefit of enforcing designers and developers to use a consistent set of proportional values in their layouts.
It’s easier to discuss and re-use values like .5rem, 1rem, 1.25rem, and 2rem… it’s much more difficult to stay consistent with values like 10px, 12px, 23px, and 31px
Bryn Jackson has written some thoughts on the 8point grid — https://spec.fm/specifics/8-pt-grid
And here is a writeup of the same process in Sketch — https://medium.com/sketch-app-sources/8-point-soft-grids-in-sketch-e8f1d5ca2cd4