Katja Grace points out at Overcoming Bias that because there is an opportunity cost to everything in life, there is a probable penalty in not having and using free time during ones student years for thinking and general contemplation.
Understanding the structure of the world and coming up with a slow plan for your life requires time, and valuable time at that. The time in question is when the mind tends to be limber and experimental (correlating somewhat with youth) and also having free space during the more productive hours of the day - mid morning and late afternoon.
It is in those moments when one is uncluttered by more rudimentary concerns that deeper insights can come out. And to launch oneself into a career or down one particular canal without much thought has a big cost in itself, and thus there is an immeasurable value in having free time at this key moment.