The reasons for pursuing a doctoral degree are as varied as the fields in which you can earn it. With that in mind, it is hardly fair to limit this discussion to Philosophi Doctor (Ph.D.) degrees; similarly advanced degrees include the Doctor of Science (D.S.), Doctor of Musical Arts (D.M.A.), Theological Doctorate (Th.D.), Educational Doctorate (Ed.D.), Juris Doctorate (J.D.), Doctor of Juridical Science (S.J.D), and more.
In the United States, and in many other countries whose systems of higher education are rooted in the English and German styles, the Ph.D. is a researcher’s degree. Indeed, one is earning a degree in the “philosophy” of their field. That said, many people with this degree enjoy careers in academic research and commercial research and development. In many places around the country, depending on the field of study, a Ph.D. is also required to teach at the undergraduate and graduate levels.
The process of earning a Doctor of Science degree is often very similar to that for earning a Ph.D., but with less emphasis on original research. Such a degree is often called a practitioner’s degree or an engineering degree because it is a degree of practicum, not philosophy.
In the musical arts, highly trained composers, historians and conductors receive the D.M.A. While this degree is certainly not a necessity for a fruitful career, those choosing to stay close to academia will earn this degree. Similarly, theologians and religious historians with a Th.D. are more often found in the classroom than the pulpit.
People who study education may earn the Ed.D. which, like the D.S., is a degree of practicum, not of philosophy (or research). Such a degree is particularly useful in educational administration at the superintendent and college administration levels. People who have earned this degree along with a specialty in a particular academic subject may also become curriculum directors for school districts, universities, and textbook companies.
The Juris Doctorate is earned by lawyers. Unlike the other degrees mentioned above, but similar to the Medical Doctorate, the J.D. is a professional degree and is not a terminal degree in law. Rather, the S.J.D., an academic degree, is the highest level of education in law, but a degree earned by a relatively small number of people.
In general, if you want to pursue a career in higher-level academics or as a researcher in a particular field, a doctoral degree is worth pursuing. These degrees takes years of study beyond the bachelor’s level and by themselves are not particularly lucrative (save the law degree) in the public marketplace. They can open many doors for possible careers, but be aware that some doors will also close due to the high cost of employing such a well-educated person.