TailwindCSS provides utility classes.
With tailwind, you use these utility classes in your HTML instead of writing CSS.
One of the reasons to use utility classes is to compose things in a UI that gives you the option to add classes to components for low-code building.
Responsive utility classes allow you do responsive design in these types of components. Otherwise, you might add a class in the UI and then style it in CSS.
Tailwind uses design tokens, which help enforce consistent use of styles and spacing.
One of the reasons I don't totally love tailwind is that you need to learn an extra layer on top of CSS. When working alone I have my own site structure in mind and can make decisions about where in the cascading layer I want to make a change to have a wide or specific effect. I can use my own tokens or add new ones when I see fit. But on a team, the extra structure helps keep things in order.
Arbitrary properties
https://tailwindcss.com/docs/adding-custom-styles#arbitrary-properties