It is a philosophical debate about the relationship between HTML and CSS.
The "traditional" approach to authoring HTML and CSS is predicated upon on idea of separating concerns. The idea is that your HTML should not depend on your CSS, and your CSS should not depend on your HTML.
The "utility-first" approach reacts by claiming this is wrong. It goes on to reason that either HTML depends on CSS or CSS depends on HTML, but neither are independent. This is what Adam Wathan calls "dependency direction."[0]
The "traditional" approach to authoring HTML and CSS is predicated upon on idea of separating concerns. The idea is that your HTML should not depend on your CSS, and your CSS should not depend on your HTML.
The "utility-first" approach reacts by claiming this is wrong. It goes on to reason that either HTML depends on CSS or CSS depends on HTML, but neither are independent. This is what Adam Wathan calls "dependency direction."[0]
0. https://adamwathan.me/css-utility-classes-and-separation-of-...