Many people look on genealogy as a pleasant hobby. It can be great fun to research and document your family tree. Some people even find the pastime mildly addictive. But there can also be important reasons for such research.
Determining who your ancestors were might have considerable legal and financial implications. In cases such as this it might be necessary to use DNA to prove relationships.
If you are not just researching for fun as a hobby it might also be advisable to use a professional genealogist.