By Felicity Duncan .Alibaba founder and touring billionaire Jack Ma recently came under fire for his endorsement of the 996 week – working from 9 am to 9 pm, six days a week. He called the 996 workweek "a blessing" and said, "It's a great honour to be able to work from 9am to 9pm, six days a week, because many companies and people have no chance to do so, even if it is their wish to do so.".Ma's words provoked a storm in China, where the issue of working hours is being fiercely debated. But many Western corporate titans think along similar lines..___STEADY_PAYWALL___.In industries ranging from financial services to tech, employees routinely work far in excess of 40 hours a week (the usual legal working week in developed economies). At America's top banks, law firms, and tech companies, employees routinely work around 100 a week with no overtime pay. Long work weeks are becoming the norm in many industries..But does this actually make sense? Is it a good business practice? Does it boost productivity and result in better outcomes for workers and corporations?  I think not..Employees.First of all, let's look at this from the workers perspective (I'm talking specifically about employees here – entrepreneurs are a separate category that I'll address below)..On a basic, financial level, working excessive hours with no overtime isn't the smartest move. Let's imagine that you are a banker in SA, earning R450,000 a year. Your contract has you working 45 hours a week, and you get 21 days of paid leave. Let's assume you take 20 days off (four work weeks). That leaves you contracted to work 48 weeks at 45 hours a week – a total of 2160 hours. Your hourly wage is R208 for each hour work. That's ten times the national minimum wage of R20 an hour..But, let's say you are a hard worker. Let's say you work Jack Ma's suggested 72 hours a week, for a total of 3,456 hours a year (not unrealistic at all, I know folks who work from 7am to 8pm every day at Investec in Joburg and take work home for the weekend). Your salary has now dropped to R130 an hour. That's still good money, but it's nearly a 40% pay cut. In other words, your employer is paying you 40% less an hour than you implicitly agreed to. Each unpaid hour worked is a pay cut..Now, you may argue that it's worth it because you're going to advance in your career and make even more money. That's true. But you aren't necessarily factoring in all the costs of that progress..Read also: Retire at 55 and live to 80; work till you're 65 and die at 67. Startling new data shows how work pounds older bodies..Studies consistently show that every additional hour worked beyond 40 carries a health cost. A meta-analysis of 52 studies on the impact of overtime and extended shifts found that longer workweeks were associated with negative health outcomes ranging from more smoking and alcohol use to higher risk of heart attack to more injuries like back and neck pain. Working more may make you richer, but it will also make you fatter and unhealthier. And, of course, there are the costs associated with lost opportunities for time with family and friends..By providing free labour to your employer, you're helping the company boost profitability. The costs of that extra profit are borne by you in the form of worse health, lower hourly wages, and lost time for your friends and family..Employers.From the perspective of an employer like Jack Ma, this looks like all upside. He gets hours of free labour and his employees pay the price. But it's not that simple..First, studies show that extra hours of work are not necessarily associated with greater productivity. In fact, it's often associated with declining productivity. That's because longer hours dramatically increase the risk of errors, and reduce workers' cognitive abilities, energy, and ability to focus..Consider this essay on "crunch mode" – the practice of having software techs working 70 hour weeks ahead of a deadline. Entering crunch mode yields a short-term productivity boost that quickly deteriorates as errors and bugs creep in and techs have to revisit work they've already done to fix errors (while introducing new ones again because they're tired)..The same has been found at places as different as construction sites and hospitals. More hours mean worse work, which is expensive to fix and reduces productivity. In hospitals, it kills people. Schedule your surgery for the start of the shift..In addition, longer hours are associated with higher staff turnover and increased sick time. When they work too much, your workers will start getting sick and taking time off. This, again, reduces productivity. And staff turnover is very expensive. It costs between 20% and 200% of a worker's annual salary to replace them, depending on how skilled the worker is. That cost will quickly erode all the savings you've made on free labour..What about entrepreneurs?.People like Jack Ma, Chinese tech entrepreneur Richard Liu (founder of JD.com), and Tesla CEO Elon Musk work all the time. They are passionate about what they're creating and they want to work on it all the time. Musk was sleeping at the office most of last year..Read also: Elon Musk fights tears as Tesla tweet takes 'excruciating' personal toll – New York Times .So, does this rule about too much work not apply to entrepreneurs? Well, I would say it should. As Musk's example demonstrates, passion does not preclude mistakes and excessive hours can mean errors ranging from false and misleading statements to missed targets. Entrepreneurs are humans too, and subject to the same risks of burnout. Many businesses fail, as we know. Part of the reason may be that owners work too much, too long, and start to make mistakes and bad decisions..We all need time to rest and restore our energies. Ignoring that need doesn't make you tough. It makes you inefficient.