Chrome Dev Tools let you simulate shit internet connection (2G, slow 3G, fast 3G, etc.) and Google encourages to this for development for the reasons you've mentioned.
It's awesome it exists, but useless if nobody uses it. I think the Google homepage is the only Google product I'm aware of that loads fast, minimal CSS and still loads without JS. Even on a modern computer, some websites have become completely unacceptable to run in the background (i.e. Facebook).
Installing NoScript and blocking external CSS was the best decision I ever made. Now use <25% of the RAM and <10% of the CPU I used to for the same number of tabs (in Firefox) - with a better experience because the browser isn't constantly trying to die.
