Flexible work has had some notable setbacks lately. Yahoo unleashed a flood of commentary by banning telecommuting while CEO Marissa Mayer attempts to turning around the ailing company, while Best Buy killed off its "Results Only" policy for non-store employees.

The forces of old school regimented, in-office work appear to be on the march, but not every fan of flexible work is retreating in the face of all this bad news. On LinkedIn recently, Ciplex founder, 30 Under 30 entrepreneur and occasional Inc. columnist Ilya Pozen took a stand not only for some flexibility but for extreme flexibility-- set hours should be eliminated entirely for knowledge workers, he argues.

Of course, there are many businesses for which this doesn't apply. A restaurant can't have servers wandering in halfway through dinner, stores won't sell much stuff if no one bothers to show up to work the cash register and home health aids need to coordinate so grandmothers aren't left alone. But if your employees are knowledge workers, it's time to put an end to clock watching, clams Pozin, who offers four reasons:

They’re productivity killers. Setting specific time parameters for your employees ties their success to when they come and leave the office--not what goals have been met. Productivity isn’t tied to the presence of an employee. Simply being seated at a desk or attending a meeting doesn’t truly mean work is being completed. Let's face it: filling the requirement of being in an office is far from motivating.

It doesn't build trust. Employees should passionately want to meet their goals. Let them do it in the ways they see fit. That way, they’re more likely to own their work and desire to be the best they can be.

It's distracting. It’s highly unlikely that your employees’ tasks fit within a 9-to-5 schedule. So why do you want them to be stuck thinking about how many hours they clock, rather than meeting their goals?

It works against teamwork. Having individual team members bound by set hours often produces issues regarding who's pulling their weight. Instead, let your employees focus on meeting team goals and collaborating to make it happen. This can mean a team effort in the office during the same hours or working individually in divided chunks of time.

His argument, in essence, rests on two pillars: the best motivation is intrinsic and creativity and energy are lumpy, rather than steady. If you buy these principles then eliminating hours should follow on naturally from there.

If you haven't eliminated set working hours for your team of knowledge workers, why not?