I think you do what makes sense economically for the marriage.
If your mate is planning to be a doctor, CPA, or some other profession that generally pays "immediately" more than what your career options will with your degree then you let them finish their program first. This should also allow the second person to pursue their degree with less economic stress. Marriage is less about (You & Me) and more about (Us & We).
The most important thing these days is to get a degree that justifies your time and financial investment. Nothing is worse than getting a degree and having ($100k in student loans) while ending up working as a waitress or waiter.