Because people need to know what they may be likely to get in terms of diseases and conditions. Also with things like surgeries and stuff it will better help doctors know what happening if a problem does occur and it can also help them fix it easier and more efficiently.
You would want to know early on if deadly disease runs in your family, because it may be hereditary, and you will have an increased risk of obtaining the deadly disease, due to your family history and gene traits.
