When deciding whether to buy, sell, or hold a stock, investors often rely on analyst recommendations. Media reports about rating changes by these brokerage-firm-employed (or sell-side) analysts often influence a stock's price, but are they really important?Before we discuss the reliability of brokerage recommendations and how to use them to your advantage, let's see what these Wall Street heavyweights think about Marathon Petroleum (MPC) .Marathon Petroleum currently has an average brokerage recommendation ...