Actually, when I first tried CHDK I really wanted to get the default script back after selecting something else as well. This was because I kept trying to take pictures in alt mode by accident (without knowing I was in alt mode or not quite having figured out what alt mode really is yet), and having an empty script was a great way to prevent confusion and spurious shots.
To be honest I still do that sometimes after exiting CHDK menu, but for most of the time I now know whether I'm in alt mode or not (I usually don't look at the display if I think I know what's there and sometimes I'm just plain wrong
).