Chapter 12 talks about the importance of evaluation. It also states how important it is to get as much evaluations because it is the basis of what the next upgraded or even different design will be. It is also important to understand how to interpret evaluate, especially ones that are more or less based on a emotions. Even though they may seem very bias, they are just as important as well. it is important to also use one of the three approaches, the usability testing, the analytical evaluate, and the field study.
Chapter 14 talks more in depth about the different types of evaluation. How they work and how to apply them to the design eval.
I think that these are key to understanding how to improve your future designs, it helps especially with bias. Because you may make a project bias toward a certain group, and be totally unaware that you were being bias. It also helps you take constructive criticism better as well.