Analytics tools allow you to track what keywords are sending you traffic, what keywords are profitable, and what keywords lose money. As soon as you start tracking results your campaigns get more efficient because you start focusing on the results. Tracking where you already rank does not alert you to potential areas of opportunity that you have not yet focused on, but if you track conversions you know what those keywords are worth, and it is easier to rank for keywords related to words you already rank well for than it is to rank for a whole new basket of keywords.