In science, it’s good practice to figure out how many experimental subjects you need to study in order to reach the conclusions you want to reach. Doing this work upfront ensures that you enroll the correct number of patients in a drug trial or college students in a study on how first-person-shooter video games improve visual perception (they do!).
Basically, it gives you the confidence to believe in the results you obtain after the experiment is done.
In fantasy sports, we would love to know how many games we must see to believe in who a player is.