Sometimes an autopsy will be performed if a person died unexpectedly, was in otherwise good health, or died after a routine surgery, procedure, medication, etc., especially if they were a young person.
And sometimes the cause of death is known without an autopsy - the person had cancer or some terminal disease for example.
But there are times when a family member may die unexpectedly and the only way to get answers as to what happened and why is to request an autopsy be performed. A pathologist will examine the body and review slides microscopically to determine the cause of death.
How can this help you? If your loved one died due to a genetic condition or some preventable cause, this can help you and your family get medical attention and specific knowledge of your family health history. If a patient dies because of bad medical care, one of the elements to prove in any medical malpractice case is the cause of death - and autopsy findings can be critical evidence.
If a hospital or medical examiner won't provide an autopsy, families can obtain a private autopsy - this just means they pay a private pathologist to perform the autopsy. Most hospitals have lists of local pathologists who perform autopsies.