There are two different ways in which social simulation can help a researcher - by honing their intution about how certain models and mechanisms (roughly what Polanyi meant by "Personal Knowledge") and in demonstrating hypotheses that might be interesting and relevant to other researchers in the field (roughly what Popper meant by "Objective Knowledge"). Both are valid goals and useful, indeed I would argue both are essential to real progress in social simulation. However, too often, these are conflated and confused, to the detriment of social simulation. This talk aims to clearly distringuish between the two modes, including the different ways of obtaining them, their different (and complementary) uses as well as when and how these are appropriate to communicate to others. In short a "model" of simulation usefullness is outlined with implications for the method of social simulation.