Because losing is just so much fun. EMR asked me for an explanation how to play the game. I tried typing up my own, but it started to look like a badly-spelt novel. So, I'm just gonna link the one I used: http://df.magmawiki.com/index.php/v0.31:Quickstart_guide I also advice you to use a tileset, like Ironhand: http://www.bay12forums.com/smf/index.php?topic=53180.0 They make stuff way more clear.
if you are getting too many annoying animals(especially cats), it's handy. If you have goblin invaders, it's handy. If you have annoying nobles(who occasionally demand ridiculous stuff), its handy.