Once you get over the small learning curve, it gets to be VERY productive. Think of it as writing CSS at a slightly higher level of abstraction. That abstraction being in not having to edit two separate files or areas of your HTML document (unless you want to abstract further with @apply).
Not having to go through the 'define identifier in element, then define in StyleSheet' workflow. With Tailwind you get the most commonly used style definitions pre-defined. But not so high level that it LOOKS pre-defined. Giving you room to customize greatly. How could it not be faster?
I recently completed a theme in Tailwind, mostly to get the hang of it: https://planflow.dev/free-themes/. And managed to go from idea to finished theme in about 4-5 days. That's the fastest I've ever done it.