Why is it important for the medical schools to know you have a hobby?

It's important for the medical interviewers to see that you can handle the stress of getting through the vast amounts of information you have to absorb in the course of your degree. While A level may seems hard enough already to certain people, and some may not find a hobby too necessary to keep up their spirits, in medical school you need to know how to care for yourself, and the interviewers want to know this. Part of the solution is caffeine, but this the interviewers are happy to assume you will pick up along the way.