Here are the reasons.
1. He knows the questions asked in the past few years – he will share those with you so you can prepare better by yourself.
2. He knows the ‘model’ answers, and how to best present them – he will share those answers and coach you to present them well
3. After the interview, he will give you a candid assessment of how he thinks it went – his feedback will be useful for the next time (although hopefully you get in and do not need to reapply)
I felt that I received the best interview preparation from Sandy, and I highly recommend him.
HBS class of 2012″