Mainly to identify the good stuff. So let's take the example of the subject political economy. Political economy has a rich philosophical tradition. You start at Hobbes, then you've got Locke, Rousseau, Smith, Marx, Ricardo, Mills, Keynes, Hayek, Friedman... Each of these philosophers cites a previous philosopher and has transformed our thinking of political economy in some way. You cannot just ignore all of them because then you'd have no clue about how the world came to be the way it is and when you read contemporaries you'd have no frame of reference. So, who do you eliminate?
