Let me try to clear things up. A Cohort study is a particular type of study generally used in the medical field to link causes with effects over time. The pictures you provided in your original question appear to be exactly this type of study. I may have gone a little further in breaking down the exact type of study you meant.
A case control study on the other hand is a study type where particular cases are selected for review are taken along with a control group. For example, selecting people taking a medication and then comparing to see if they have more birth defects compared to people not taking the medication.
The random nature of your case scenario means it is a cohort study designed to long term health care questions. The pros and cons of the study remains the same. Cohort can have disputed results due to other concerns being present the researcher is not aware of. In addition, merely being part of a study can encourage healthier lifestyles and effect the natural results as well.