The use of Reality Check serves two purposes. First, it is written record of things that were assumed must be true for a model to make sense. These are things that typically go undocumented, even though they may be the most important product of the modeling exercise. Very simple insights such as the notion that if the yeast keep growing they will eventually run out of water are really important things to understand about a system.
The second important thing about this example is that it illustrates a way of building models that is both effective and relatively efficient. You start from a basic core and then add the complementary structure necessary to get conformance to Constraints. This provides a rigor and direction that can increase greatly both the speed and quality of modeling work.
