Is it worth killing the Training Robot?
Winning in a training battle increases the damage of your attacks. It's barely noticeable at the beginning, started to see a change - about 1 point per victory - around the middle of the thirties.
As far as I can tell, you get as much gold as the robot has hp every time you win. I have a diamond sword with 405 damage, and gain about 470 gold per round. Coincidentally, my robot has that amount of hp... ;)