From Science:
When I was first employed by a government research organization some years ago, my supervisor, although bright, kind, and productive, was so committed that she regularly labored into the wee hours of the morning and on weekends. She rarely took vacations. No one who worked with her could keep up with the pace, certainly not me. Typically, I would leave work at about 6 or 7 each evening after crossing off most of the items on my to-do list. Invariably, when I returned the next morning before 8, my in box was overflowing.
Lacking control over my workload, I felt stressed. My productivity suffered, as did my morale. Other employees became so dispirited and worn out that they left. (These were days when jobs were abundant.) Nonstop work–without sufficient downtime for family, friends, and solitude–violates the natural rhythms of life and nature. My supervisor was a perfectionist: obsessive, competitive, extremely mission-driven, and excessively failure-aversive. These traits made it difficult for her to set healthy boundaries between work and the rest of her life. And those traits affected not just her life but also the lives of all the members of the team.
More here.