When responsive design and development became very prominent and a very obvious choice to adapt, people started to take notice of the 'rem' and 'em' units. Just in case you don't know what that is, the simplest way I can put it is that is a unit base on your base font size. So if your base font size is 16, 1 rem is 16, and 2 rem is 32. 'em' units work the same way, except that with the font size of the parent of the element, the 'R' is the difference, that stands for 'root'.
Anyway, when you look up best practices for the development of a responsive website, most sites will tell you to use rems. And I did, and I did not like it.
The first issue I encountered was, of course, doing the math, so I built a SASS function called px-to-rems() to do that for me, and I continued my development not paying that much attention to it.
Everything looked fine, but when I took a close look to the designs, the font size was the same as in desktop, which makes sense, since it is a smaller device, you might even want a bigger font size. So I ended up loosing the function and sticking to regular pixels.
I think we focus sometimes TOO much on reusing styles, that we go a bit over the top, and it loses purpose and stops making sense. At least for me.
Maybe I just haven't learned the proper way to use this magical units, but for now, good old pixels are my favorite.