I run a market making bot.  It maintains orders on both sides of the book at 1.3% intervals.  When my buy orders are filled, it places a sell 1.3% higher.  When my sell orders are filled, it places a buy 1.3% lower.  I lose out when it trends continuously, but it stabilizes price and I turn a profit when the bulls and bears duke it out.  By keeping orders on the book, I help make it possible for companies like bitpay that need to accurately price and immediately convert bitcoins to USD and companies like bitinstant and coinbase that need to go the other way.