Ahaha...yeah UCSF had a 15 min essay on "If you could go anywhere for 10 days, money not an issue, where would you go and WHY?"
I think it's just a question of seeing how well you can articulate your thoughts on paper, and also an attempt at seeing how you write in person. They don't know if you really wrote your essays or not, so it's a way for your voice to show through in this quick writing sample. I doubt it weighs much in the overall process, though if your grammar is terrible they might take note of it.