A cohort-based model groups individuals with at least one common characteristic over a period of time through a state-transition process. A population-based model reflects as much information as possible about a demographic of the target population. Based on these definitions, a population-based model should be preferred because (1.) the population model does not focus on a specific representative demographic and (2.) the population model is dynamic in the sense that it captures the entry of new groups to the target population.
My question is what the advantages of are using a cohort-based model over a population-based model are in the context of modelling mortality specifically in the management of longevity risk. Furthermore, how should a person choose between cohort and population model when designing a mortality model.