When you are building a website with a css framework like Bootstrap, you will only use a part of the framework and unused css styles will be included. Purgecss removes unused selectors from your css, resulting in smaller files. "With PurgeCSS, you'll have a hard time generating CSS that isn't under 10kb minified and gzipped." - Tailwindcss docs
Looking beyond Purgecss to tidy styles? Try Unused CSS for scanning and purging, or pair Tailwind with DaisyUI for prebuilt components. Need color help? Coolors and UI Colors speed palette creation. For visual tweaks, CSS Pro reimagines DevTools.