Another advantage is speed.

I did a proof-of-concept last week with MVP.css and it was so quickly put together that it was almost as convenient as from writing the content in a Google Doc (where I use borderless tables for the columns). Google Docs are usually my second step in the process, as I don't like to get feedback on sketches, but this might be it now. (My first step is that I sketch on receipt paper, it's the perfect width for mobile, super cheap, and can be as tall as you'd like for your design. Highly rec.)