I'd imagine you get more redundancy (in the good sense) by having more part-time people, lower your truck-number, and have people less likely to be distracted by personal stuff in work hours since they can visit the bank (etc.) on their free days. Recent posts about productivity have claimed white-collar/creative workers are most productive at lower than 35 hours a week. I wonder if anyone has actually studied the cost/benefits from both the employer and employee side.