Breakpoints have risen from obscurity and taken center stage in the life of the modern Web designer. They are necessary because they enable us set thresholds for our design aspirations. We live in a world where the Desktop Computer is not the only device holding sway, so we have to be cognizant of this reality and update our tactics to ensure that the Websites we build can work everywhere for everyone.
However, the tools that come standard for building these so-called Responsive Websites [Media Queries] do not really make it easy to target Device Classes like Smartphones, Tablets, TVs, etc. I find that odd because it seems like Device Classes should be logical breakpoints in every respect. I say that because when starting out, it's virtually impossible for you not to ask the question "How is this Website going to look in a Tablet?!"