Nope. Not at all.
On average, per website, you could be doing, say 2000 or more tests or 2000 needless mouse movements and clicks!!!
It's good exercise for my finger.
Combine that will closing the browser window then you could be looking at say 3000+ needless mouse clicks
There's no need to close the browser. I just keep it open.
Wouldn't it be more time-efficent for the browser to give you a preview in real-time?
Possibly, but it's not a biggie for me. Although you can do this with your browser anyway. Using Chrome dev tools, for example, you can add styles and HTML in real time, and then save this to your files when you are done. (Soon this will be automatic—but for now I think you can only do it with JS.)
Have you never considered using CoffeeCup? or something similar?
I've considered it, and tried a few things like that, but didn't like them. I also don't trust the "live view" in programs like this. Dreamweaver's Design View, for example, is very unreliable. The only real testing ground is the browser itself.
Adobe is working on a code editor that does this, called Brackets, but it's at an early stage right now.