For me, the main attraction and benefit of being in grad school was being immersed in an environment filled with smart people wanting to "do more". My school's heavy emphasis on entrepreneurship has also energized me about creating a startup. The caveat is that one must find a way to attend grad school for free (which actually isn't hard at all).
So will you now tell me why they should start a business instead?
I can tell you about this experience at great length if you really want. ;)
(Dabbling in medicine or law is particularly expensive, because... it's expensive. You have to go into massive debt, on top of your potentially massive college debt, before you figure out that medicine or law can be a really miserable line of work. At least I didn't do that -- my years of career trial-and-error were cash-flow positive, though I didn't exactly live like a prince on my grad-student and postdoc salaries...)
Meanwhile, you don't have to do years and years of academic hoop-jumping before learning whether or not you'd enjoy starting a business, or working at a startup. (Or working at a big company, for that matter.) You can learn a lot just by trying it. You don't even have to wait for graduation.
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[1] Beware: You may think that you can learn whether you'd enjoy (e.g.) archaeology by volunteering to help on a dig, or by being a grad student in archaeology. And that is a good idea. But enjoying life as a grad student or intern is not the same as enjoying a career in a given field. In many fields, professors spend most of their time raising money, managing people, playing political games, and writing papers and proposals, not digging holes, performing calculations, or building neat stuff in the lab.
And if you enjoy being a grad student, then there's little disincentive (other than opportunity cost) not to do that, learn a lot, and come out with a PhD that will make it easier and better paid to find similar work out there.
(n.b. I am assuming that one is getting a PhD in the sciences, or any field where there is reasonable amounts of funding available and one need not take loans to continue being a student.)
Doing a startup might get me financial independence, but only at the expense of possibly years and years of grinding effort, given the normal stats.
However, if my standard of living is low enough, and I pick my location well, I should be able to become financially independent in not too many years at a normal job.
Additionally, if you put a few years into the military, you could even get a free grad degree.