well this is as vague question as asking "how can you benefit from chemotheraphy" - if you get sick by the particular sickness, it can help you. Human genome sequence knowledge is good for gene...
The Human Genome prodject was created for the prevention of diseases due to Inherited genes passed on to the offspring of a disease carrier. The New MrSpock (Xbox Live Gamertag).
Generally speaking, scientific knowledge is a good thing. The only real disadvantage to the human genome project is that it was quite expensive. One could always argue that the money would have been...