The preffered patter to learn from is the one we are proposing in the exercise. The general idea is that we are teaching a pattern for the Next-Best-Action implementation. For this, usually you need to use a switch rule where you arbitrate at high level between a set of business issues.
Concretely in the exercise we are asking you to 'shot-down' retention, which means the easier is to remove from the switch rule. If you aresked to put it back at later stage the only thing you need to do is to modify the switch rule again. Also, imagine if the switch rule would arbitrate between multiple business issues, not just two as presented in this example. You would always want to have this centralised switch compoenent for arbitration.