Do you know how you can benefit a lot when you spar with those much junior to you?

A special feature of our school is that the same class may have participants of vastly different skill levels. Junior participants will of course benefit much because of the presence of seniors. But are the seniors wasting their time re-learning material that they already know very well? Actually, the seniors benefit more. Do you know some of the reasons? One important reason is that they can try out skills and tactics on the juniors.