Depends on the program and the school. If it's not necessary to give up a job or reduce hours, why do people still do it? And why do schools provide stipends to Doctoral students, to offset (at least somewhat) that reduced income (opportunity costs). It's not out of the goodness of their hearts. It's to get more people into programs that require F/T campus attendance - and still earn tuition revenue. That's a clawback that works for the Uni. Rich Douglas holds a PhD. Not every person who holds a PhD is Rich Douglas.