Microsoft Japan made headlines a couple of weeks back when it announced that its experiment with a four-day workweek had resulted in a 40 percent surge in productivity, but Microsoft is far from the first company to see greater success when employees worked less. From American tech startups to Australian marketing firms, a ton of organizations (and even cities) have recently shared their shortened work-week success stories

But while evidence is mounting that most employees work inefficiently and can actually achieve more when nudged to compress their work into fewer hours, one expert is warning bosses considering making the switch to a four-day workweek not to get carried away. 

As time-management expert and author Laura Vanderkam explained to Business Insider recently, while compressed workweeks make employees happy and productive in the short term, they have one big downside in the medium and long term. Leaders need to be aware of this pitfall to avoid it. 

There's more to work than ticking through your to-do list

What's this frequently overlooked problem with a four-day workweek? "People do the immediate stuff of their job that has to get done, but then you wind up shortchanging kind of the longer career-development stuff," Vanderkam tells BI

In other words, while 30 hours a week or so might be enough to get through all your most pressing tasks, there is often not enough time left over for less urgent but highly important things like training, learning, and big picture thinking. 

This isn't to say Vanderkam is completely skeptical about cutting down on Americans' comparatively long hours. "I think there are definitely arguments to put a cap on hours that have been inefficient before," she says, but she adds, "I think there's also a point where you cannot be more efficient without really losing some of the higher-value things that are important but not urgent."

Reasons to believe she's right

There are plenty of reasons to suspect that Vanderkam is right to be worried that employees may shortchange important but not urgent tasks if their hours are cut. Leaders like Bill Gates (who was famous for his Herculean work schedule earlier in his career) already say they struggle to find time for big picture thinking amid the everyday hustle and bustle. That's why, back when he was Microsoft boss, Gates famously scheduled "think weeks" away from the chaos. 

Creativity experts also warn that breakthrough ideas almost always require long hours of incubation and intellectual noodling. Big ideas also tend to arise from connecting disjointed bits of information in unexpected ways, which means somewhat aimless exploration often contributes to their development. In short, creativity suffers when everyone is busily working away on a tight schedule. 

Finally, a stack of studies attests to the phenomenal benefits of lifelong learning. And I don't think most of us need an expert to tell us that learning is one of the first thing to fall by the wayside when you're crazy busy. 

The correct way to cut your team's hours

All of which leads Vanderkam to argue that giving employees more flexibility and control over their schedules beats a set reduction in hours. She makes a solid point. But I don't think her opinion is necessarily a death knell for shortened workweeks. 

It's quite possible to hold open space in your schedule for activities with a longer time horizon even within a reduced workweek. But to do that, managers need to be aware of the danger of these activities being crowded out and actively encourage people to value and make space for personal development, idea marination, and other tasks with a less immediate pay off. 

By pointing out this pitfall, Vanderkam has nudged them to do just that.