I used the JIT version recently on a new landing page with code completion for class names in my IDE and found it great. The distance between what I'm picturing in my head and what I have to type to see that on the screen felt so much shorter and less fatiguing than the standard CSS approach.
With the regular way, to style something that's probably not going to appear elsewhere, I'm having to: come up with class names, annotate the HTML with them, repeat some of this annotating in a CSS file, jump back and forth between files to tweak the styles, use the web inspector to figure out which CSS class is overriding another then jump to the right CSS file to fix it etc.
Tailwind classes are also faster to type and flip between when you're experimenting (e.g. editing "mt-5" to "pb-3" vs "margin-top: 4.25em" to "padding-bottom: 2.75em") and you get less distracted because it has sensible defaults and helpful guardrails (you rarely need all the possible attributes and range of parameter values CSS has available).
I also rarely had the super irritating and common CSS scenario where you edit a style and it doesn't change and you have to go investigate to find out why e.g. something is overriding something, your selector is wrong, and even after all that maybe you undo the edit because it doesn't look good. Plus you no longer have the fear that tweaking a shared class to going to break some completely different page.
I feel that beyond some building blocks, trying to create reusable CSS classes with cascading styles has similarities to using excessive abstraction and deep OOP class hierarchies in regular programming languages to avoid a little duplication.
I also don't have a problem with styling stuff appearing in my HTML files either as long as the right HTML tags are used around the data. HTML files are already full of class annotations and divs that are only there for styling yet this doesn't cause a problem to e.g. browsers, screen readers or crawlers.