No, I have HTML and CSS in the same component file. I prefer having styling in one place (the CSS inside the component file) rather than two (the HTML of the component and tailwinds’s own postcss files that implement the styles).
Standardised and clean CSS syntax. The benefits in that context are debatable, a component based frontend architecture is where it absolutely shines. If you end up using it in that context you won't need to ask this question, it quickly becomes clear that it's the optimal path.
What can't pure CSS do here and that Tailwind does ? The CSS syntax is already clean and standardized if you use it properly and don't name every little piece of interface. It is a genuine question, by the way...