Maybe your school thinks it is a way to get your competitive juices flowing by comparing scores with your peers and driving motivation by seeing where you are weak.
For the OP, file this one as one of those decisions that you can spend forever rationalizing/stressing but in the end will make little difference whatsoever in your final score.
I took an NBME on day 0 with a couple of friends. My rationalization was that I wanted to know exactly what I was up against. We all received passing scores and it was a great confidence boost for us- we knew that with zero studying and six weeks left to go we were already prepared enough to pass the beast. I felt really confident and more enthusiastic heading into those first 2 weeks thinking I would get a great score. I felt like I had a better grasp on the kinds of questions they would ask and the difficulty level (much easier than UW/Kaplan blocks which can kill your confidence)
I also rationalized that it would help me know what my weak spots are (although in retrospect I have serious doubts about NBMEs or the real thing identifying strengths/weaknesses... my only non-star was in one of my stronger subjects).
I figured there's nothing to lose (except $40) by taking it early. Even if I had failed or gotten a marginal score, I'd still be able to say "well i haven't started studying yet!" If you were to take it after 3-4 weeks after studying and did poorly... that would be very depressing.
