At my university, students who are almost through with their degree requirements are allowed to march in graduation. Graduation pictures, celebration, etc... but not there yet. This does not insure they fulfil those requirements, or that they receive the degree. At MIT, I gather that those who march are checked to be sure they are actually ready to receive the degree.
Once you actually receive the degree, you can change your license plate to DR SMITH, or SMITH PHD, or... Your email address can say whatever you need to say, firstname.lastname@example.org. But before then it makes no sense. It is a mockery of yourself, for until you have the degree in hand, you are a cartoon.
As for marching at graduation, despite being permitted to so march, you want to march when you are done. You want to be hooded, if this is a doctorate, when you are done. (Otherwise, you are more like the a cartoon of the Ku Klux Klan, albeit in black than in white.)
Of course, if your degree is a scholarly degree, the PhD, what counts is what you do next in terms of scholarly publishing and research. If it is a professional doctorate, EdD for example, what counts is what you do with your career. The degree is just a sign of one step on your road.
If your degree is just a sign that you could do it, and for many that seems to be the case, I have little to say.