- Multi-target nuking from a single target (instead of having to click the screen) - big deal for boxers.

I've noticed, that is definitely a huge deal for MBers. I'm just curious how you do it? With macros?
The thing about chain lightning is that it doesn't need anything special at all - just hit it on your current target, and it takes others with it. No macro required.

Since the demise of the "map ping" method some time ago, I'm not aware of any way to target an area (for blizzard, etc) without clicking.