I think the purpose the author shared this technique for is when you need to constantly comment/uncomment a block of code for testing.
I agree with you, though. Once you're done with your experiment, reset the commented lines to something more conventional.
Even then, any editor worth its salt supports comment toggling with a single keystroke anyways. Good editors (vim, cough) can even toggle lines or paragraphs regardless of cursor position.
So I agree, this hack is more trouble than its worth.
the FF webdeveloper extension is the one I find easiest for live CSS editing - though I'm using firebug more and more - it doesn't have comment toggling (it's just a text field). Such tricks are handy.
Unless you're trying to work them around CSS comment hacks!
There's a chance you'll confuse yourself (or your code reviewer or other reader) and spend an hour debugging to find what you thought was commented out wasn't. That's not worth it to save one keystroke.