Will a PhD benefit or hinder your career? Before committing to a multi-year commitment, its valid to ask any and all the questions you need to help you decide.
A PhD is a terminal degree at the highest level that demonstrates the professional at the completion of the process has the following qualifications:
Getting admitted and starting a PhD is nothing compered to the effort of completing a PhD Of course it is important to stress that the requirements vary by geographic region, one's particular institution, as well as by discipline. In many fields, only 50–60% of people who start a doctoral program might complete one. Quite a few drop out and others may reach the ABD (all but dissertation stage) but never go further. You don't want to be an ABD, do you? You want PHD instead.
Now to the second question at hand. Will a PhD. helps advance a career? the short answer is it depends. If one wants to pursue a full-time academic career, in many fields (not all) a doctoral degree is a necessity. However, it is important to emphasize that completing a degree by no means means one will be able to get an academic job. In many fields, the supply side of completed recent PhD grads is far greater than the demand from academic institutions. Particularly in the social sciences and humanities a significant percentage of grads are unable to find full-time tenure track jobs. Some do manage to obtain temporary or contract positions of a short duration, others wind up adjuncting (which can be a very challenging way to earn a living or build a career) while others go into jobs in the private sector, nonprofits, for-profits, etc.
In considering a Phd. one has to do the market research to see what types of jobs are available for grads. Too many people start programs without fully researching the potential career opportunities both in and outside of academia. In addition it is important to explore the financial cost of being outside (if one is doing the degree full-time) a regular career path and salary growth while doing the PhD (basically what is the financial trade off of not earning a full salary while doing the degree and the potential financial benefits of completing the degree)
For those who aspire to academic and policy careers, a PhD in many cases is still a strong asset. But for many other careers it may not be helpful or given the the cost-benefit analysis not right choice.
A PhD will be taxing not only academically but also financially and in many cases will affect your personal relationships. Its hard for family and friends to understand why you can enjoy a picnic on Sunday afternoon and instead you need to be at the library. Or worse yet, you in the picnic not enjoying yourself for all the work that you know is pilling up. For those and many reasons, consider carefully if the investment in a PhD is worth the struggle. For everything else, there's work experience and Masters degree. Nothing wrong with those.