It's so you can restart the machine if it locks up without power cycling the machine.
What Zepher said. I think it's a real test for case designers to make it so this button is easy to use if you want to, but not easy to hit by mistake. I like designs where the reset button is slightly recessed and small enough that my index finger can't trip it (but maybe my pinkie finger can).
my rosewill blackhawk ultra case is the first one i have had that has that feature, it sits about a 8th" down and is hard to hit by mistake.
I've accidentally pressed the "reset button" on my 500R a couple of times instead of the case lights on/off button, and it seems like it should be called the "crash button."
Seriously, what's the point?
You're questioning the use of a reset button, but find use for a case lights button?! Ummm, ok...