If someone dies intestate (without a will), and there are no immediate relatives who will be able to inherit through
One of the most popular is for health reasons. Some diseases and conditions are hereditary, and if someone dies from such a disease, an heir hunter can be sent to find extended family, and potentially save their lives by telling them about the illness. They can go and get checked out, and make plans such as writing a will and organising guardians for their children should the disease be a particularly aggressive one. Cancer is one such disease; heart conditions and degenerative diseases such as multiple sclerosis are some others.
Heir hunters can also be hired to search for missing people, even if there is no inheritance involved. Perhaps they have completely disappeared, or maybe they moved away and contact has been lost. Perhaps a child was adopted, and they are looking for their biological family, or the family are looking for the adopted child. Yes, it is possible to do these searches for yourself. It would certainly save you money that way. But it will take you a lot of time and effort, whereas an heir hunter, who does this every day, will know exactly where to start and what avenues to go down. Hiring a professional heir hunter will make things much easier.