There are a few fleshed-out articles about why utility-first CSS is a good thing. However, if you're just a little curious and want a brief introduction, Chris Ferdinandi has your back.

In JavaScript, we create small, modular functions that can be reused throughout the code base to keep our code DRY. In CSS, for some reason, it’s not seen as weird in the slightest to repeat yourself a lot.

Utility classes help keep CSS DRY.

The stylesheet for my website is so small that I can inline all of my CSS still send most of the page in a single HTTP request.

Read the rest of Chris' article on gomakethings.com.

Hungry for more? Check out In Defense of Utility-First CSS by Sarah Dayan or CSS Utility Classes and "Separation of Concerns" by Adam Wathan.