They exist to make your dice rolls great or terrible exactly when you need them to be. Case and point: We were wrapping up the Pathfinder campaign, killed the prince of demons and were getting ready to start the next campaign. We turn towards the DM and as a party ask what happens with the demon's power. He has us roll for it. I'm playing a Gunslinger who wants to be emperor. My friend is a witch, and my other friend is a cavalier; they have less grand motivations. Witch rolls up: its a 1. Friend rolls up: its a 1. I roll my dice, just let it flow on the table: 20. End result? I absorbed the power of the Prince of Demons, with no consequences to my personality or moral compass. The Dice Gods smiled upon my character that day. Praise be upon them. This is why you never let people touch your dice.