I can understand the need for breakpoints. What I am trying to understand is why have the fixed points where they are. Why at 499px (when working on Mobile up)? And why not at 499px when working desktop down?
I also notice that in RBB/3 there are 3 fixed breakpoints and RBB/4 has 4 fixed points - even as wide as 1200px which is outside the screen size of both my desktop screens and that of my standard 15.6" laptop.
Back to the question - not why they are there, but why at the points where they have been placed.