Longer working hours don't' guarantee quality

The headline certain gets your attention: "Smartphones and tablets add two hours a day to the workday".
The Telegraph reported last week that people who use mobile devices (which is just about everyone) work an extra 460 hours per year. That's a staggering 38 hours a month - a full extra week "donated" to the employer.
Quoting a survey by Pixmania, the newspaper said the average working day has increased to 12 hours as people spend 9 hours to 10 hours at work and another two making work phone calls or sending work emails.
While everyone agrees people are working longer, the issue is how productive are those extra hours, and more important, how effective are employees overall when they're putting in 10 hour to 12 hour days?
Myriad studies have found that, as overtime increases, an employee's effectiveness declines. This is not a new phenomena - it dates back more than 150 years. One common finding is that for maximum performance, the optimal number of hours per week is around 40. And that's for manual laborers - many experts say the number should be even lower for knowledge workers.
People who work 60 hours and above, and the companies that encourage such behavior, are fooling themselves in thinking that longer hours in the office, at home, or on the train, translate into a proportional increase in output. They generally don't. Employees working those kinds of hours typically arrive later in the morning, take longer breaks, reward themselves more often with non-work tasks like Facebook, personal email, sports results – even cigarette breaks. And why not, they are working so much outside of office time.
Sure, there can be significant short-term gains. An individual can push for a week, a month or even longer. But over the long term, and in aggregate, the numbers tell the same story: longer hours lead to diminished performance - output declines and often work has to be re-done.
Many of us may think we're super-efficient and that our output is steady regardless of the number of hours we work and that our passion enables us to defy the stats that state otherwise. That is unfortunate, because according to the research, we'd be more effective if we worked fewer hours.
Don't get me wrong, it's great to be able to work outside the office. It gives us much needed flexibility and the ability to finish urgent tasks on the go -, but those extra two hours a day are certainly not a net gain for the individual or company. People may be "working" 12 hours a day, but most are still producing somewhere around eight hours of output over that time.
The real issue is what are we giving up as we work those extra two hours a day on our smart devices?