According to the structural-functional approach, the one that considered as a direct benefit of disengagement from work is: It allows the next generation to transition into jobs.
Especially when a worker became too old for his job, it would be really beneficial if they start to train a younger potential replacement for him when his retirement time come.
I believe what you're looking for is economics, but I could be wrong.
Answer:
Observational method/Field experiment
Explanation:
A field experiment is conducted on a daily bases. In this field experiment, the experimenter still manipulates the independent variables.
But this happened only in real-life settings. In this experiment, the experimenter was not in that condition to control the extraneous variables. This experiment can conduct real life.
Thus Terence mentor recommends the observational method/field experiment.