Financial advisors call it "leakage," a dangerous habit that drains retirement accounts to pay for today's wants. But new research suggests that 401(k) loans are rarely used for frivolous spending, serving instead as a critical safety net for households hitting a wall on medical bills and housing costs. The research, conducted by the Employee Benefit Research Institute and J.P. Morgan Asset Management, analyzed the spending behavior of private-sector 401(k) participants to determine where loan proceeds w ...