Via NY Times:
Students who borrowed less earned worse grades and fewer credits. And most surprising, those who borrowed less were more likely to default on their student loans over the next three years. This puzzling correlation is borne out by other data. Historically, those with more student debt have been less likely to default on their loans. A plausible explanation is that more borrowing made it possible for students to obtain more education, which led to higher earnings and a better capacity to pay off debt.
Susan Dynarski