To an extent, Trammell said, policies like unlimited time off are simply marketing spin not unlike mobile "unlimited data" plans. "Sure, it's unlimited data, as long as you don't use too much."

But enabled by technology, changing attitudes about work and careers present a new opportunity for chief executives to separate their top performers from the slackers.

And an unlimited time off policy is a powerful tool for that purpose. It's also a test of employees' attachment to expensive traditional time off policies.

Unlimited time off allows CEOs to focus on their A players. In Trammell's mind, they're the ones who have to be told to take time off. They're emailing on Saturday night. They're working wherever and whenever they want, sure, but working seemingly all the time.

Trammell says an unlimited time off policy is only realistic if the company has a way to track employees. It also becomes a good measure of employee engagement and dedication.

Top employees won't put in for vacation time, so chief executives should put their attention into keeping them happy at work. Only the slackers will actually unplug and take three weeks off at a time, and it only takes a few minutes of a hiring manager's time to fire them.

So, in a way, an unlimited vacation time policy puts the burden on managers to keep employees happy, and working. If they're not happy, or working, "it doesn't matter what your vacation policy is," Trammell said, you're not getting as much from your workers as you could be.

"With technology, you can be reached anywhere at any time," Trammell said. "What does vacation really mean? It's become nebulous."