It's not just "seconds wasted in compiling". It's having my IDE say "thinking..." for 3-10 seconds every time I want to see what type something is. Or having create-react-app load for 5-15 seconds, every time I save any file before letting my browser update (even if I press refresh manually), because it's compiling. And when this happens on a minute-by-minute basis, it drastically slows down development time.