There are generally two schools (ha!) of though on the topic. First, that an MFA is two years of dedicated apprenticeship that will ultimately yield better prose. And alternatively, that writers should spend time...well, writing, and the act of writing will yield the same end result.
So back to my question. What are your goals? Do you want to teach at an institution of higher education? If so, you will need a minimum of an MFA. I say minimum because while it used to be that an MFA was universally considered a terminal, practitioner's degree, there is a trend of PhD programs in the discipline now. Savvy students will pay attention to this trend because all other things being equal, a PhD usually trumps an MFA for a hiring committee.
If your goal is not to teach, but solely publish, then an MFA is not always necessary. You really just need to write something good and cultivate contacts to market your material. Many writers do this without an advanced degree.
I will confess that while my personal MFA experience was the impetus I needed to take myself seriously as a writer, it has been seven years since graduation, and I am still re-paying my student loans. That stings. The MFA experience made me a better writer and gave me a community of like-minded people, but it was not directly responsible for any publishing success. I absolutely do not regret the experience, but is the experience necessary? No.
So the short answer is that I don't know. I can argue both sides.
That all said, it is imperative to apprentice in some form, and MFA programs are a structured way to do so. The rigor, the community, and the individual instruction can elevate your material to exquisite heights, and the contacts you make have the potential to advance you professionally. But if you opt for this path, do your research. Some programs are academically challenging, and some are less so. Talk to alumni and current students before you commit. Ask to read creative theses from graduating students and, better yet, attend readings from alumni. Ask yourself "does this represent the type of work I want to produce?"
In the end, it's all about writing something good. How you do it is up to you.
Takeaway: Articulate your goals, and you will get a clearer sense of the best path.