Cohort studies like this one have led to some major advancements in our understanding of disease - if you know anyone who takes aspirin to reduce their risk of cardiovascular disease, for example, that came out of a cohort study. There is a tremendous amount we don't know about the development of diseases in childhood, life-course trajectories, the effects of environmental exposures that need well conducted, large sized studies - the large bit is important, as they need statistical power if anything will meaningfully change in terms of policy.