If you are just doing a single page its not that different, but if you are building a web app and trying to tweak the CSS inside a modal or something that isn't there on page load it makes a difference. Instead of refresh -> click button to show modal again, it lets you see the changes as you make them.
It updates as you type which makes for a completely different experience.
I wouldn't say that's a completely different experience. It's the same experience minus having to hit save (which I'd imagine is fairly automatic/in the subconcious for most devs). I'll have to try it out and see for myself though I suppose.