I started linking component stylesheets directly in the component HTML, de facto eliminating unused CSS from the output. HTTP3 provides performance gains we can benefit from by serving multiple CSS files "just-in-time".
I've had great results since. No more unused CSS. No more minifying nor bundling. What you write is what you get. It's liberating! Hehe.
2. CSS often blocks page render, to avoid flashing unstyled content.
3. "Tree-shaking" CSS is often difficult or impossible.
Many (most?) CSS libraries minify their outputs...Bootstrap, Materialize, Semantic UI, Foundation.