We all know work-life balance is important. You want your team to have the freedom to enjoy personal and family time. In turn, you get employees who are happier and more productive--and aren't burned out.

That all sounds logical, but until recently the perceived value of work-life balance was largely based on anecdote and intuition. Well, good news: The research is in, the hunch is correct, and the solution is easy, says Leslie A. Perlow, a Harvard professor and author of the book Sleeping With Your Smartphone: How to Break the 24/7 Habit and Change the Way You Work.

In an article for Harvard Business Review, she and research associate Jessica Porter explain that, in a 2008 survey, 94 percent of employees in professional services said they work at least 50 hours per week, not including the 20 to 25 hours they spend using their smartphones outside the office.

Perlow (@LesliePerlow) also studied the Boston Consulting Group, an international professional-services firm, over the course of four years. She instituted one simple change that had a major effect on the well-being of the firm's North American employees: She required the members on some teams to take one pre-planned night off per week. That's totally off --no e-mails, no voice mail, no nothing that had anything to do with work. She has labeled the initiative PTO for "predictable time off."

One night a week. That's all.

The results were staggering. Compared with teams that did not take PTO, those who did were more excited to start work in the morning and more satisfied with both their jobs and their work-life balance. Beyond that, the employees involved in the PTO program said they were more likely to stay with the firm long-term and to perceive themselves as providing value to clients.

Meanwhile, then-CEO Hans-Paul Bürkner told Perlow that PTO "has proven not only to enhance work-life balance, making careers much more sustainable, but also to improve client value delivery, consultant development, business-services team effectiveness, and overall case experience. It is becoming part of the culture--the future of BCG."

Perlow's findings suggest that PTO policies--though they should have the C-suite's commitment and support--are best organized at the team level, with employees arranging who takes which nights off when and meeting regularly to discuss the process.