It depends why you want to do the degree. If you want to do it out of interest, and have the financial means to do so, then go for it.

However, presuming that you already have a BA or MA, are you able to get a job related to the subject area that you interested in with the degree you already have?

This question gets asked fairly regularly, and I recommend reading through this section of the FAQ for some very useful threads.

I also wrote this response to a similar thread a few months ago. I stand by my point that specialization matters a lot. There tend to be far fewer people pursuing and earning doctorates in African or Middle Eastern history than modern European or modern US history. For the last few years, that has meant that academic openings for African history jobs were close to the number of degrees conferred, while European history has been more popular, and long been overproducing degrees. Meaning lots of competition for academic jobs in that field.

However, this year the number of African history jobs are down sharply, while European history is declining more slowly. And the number of TT history jobs overall is at historic lows recently. Who knows where it will be in 8 years?

So, the American Historical Association, Chronicle of Higher Education, Inside Higher Ed and other academic institutions have been giving much greater attention to "alt-ac" careers. That is, pointing out what people can do with a history doctorate other than be a professor.

These careers in university administration, libraries or digital information, government employment, or in the nonprofit sector can all be fulfilling careers for the right people.

However, whether that is "worth it" is something only you can decide for yourself. Are you willing to work for very low wages for 8 or 9 years to earn a doctorate (most history degrees take more than 7 years), to get a chance at a dwindling Tenure Track market, short term employment as an Adjunct professor, or to do an alt-ac job?

Ask the helpful guys at /r/AskAcademia.