Netflix certainly deserves credit for introducing a family leave policy that eclipses the nation’s rather pathetic norms. Just 12% of all workers receive paid family leave nationally, and the United States is one of just three nations surveyed by the United Nations that doesn’t guarantee women pay during their maternity leave.

But in recent years, as companies compete for top talent by dangling plush benefits packages, the word “unlimited” has cropped up more and more, most often in relation to vacation days and with decidedly mixed results.

Netflix has been recognized as one of the first major companies to implement unlimited vacation days; other companies like Best Buy, Evernote, and Virgin Group have followed suit, reasoning that so long as employees get their work done, the number of days they take off doesn’t matter.

The only problem is that when workers are presented such an open-ended option, they are often left confused. For starters, it’s hard to determine how much time off is appropriate to take. Then of course there’s the fear that taking time off will mean missing out on important meetings and projects—absences that could scuttle opportunities for advancement or promotions.

Netflix stopped keeping track of employees’ vacations in 2004 to “focus on what people get done, not on how many hours or days” they work. A Netflix spokesperson told Fortune on Wednesday that the company doesn’t count vacation days. In 2011, a Netflix spokesperson estimated that Netflix employees were taking three to five weeks off annually—more than they had in the past, according to The Wall Street Journal. He also said that workers keep in touch via email or phone when they’re out. “People are on all the time,” he said.

That doesn’t sound like much of a vacation.

In announcing Virgin Group’s unlimited vacation policy in September, founder Richard Branson said in a blog post that he wants his employees to take as much time off as necessary, but he said he assumes “they are only going to do it when they feel a hundred percent comfortable that they and their team are up to date on every project and that their absence will not in any way damage the business—or, for that matter, their careers!”

No pressure! Bon Voyage!

Employees at Tribune Publishing were so outraged by the company’s decision in November to offer unlimited PTO that it rescinded the new policy just eight days after introducing it. It had caused “confusion and concern within the company,” CEO Jack Griffin said.

Taking time off for vacation and going on a maternity or paternity leave are no doubt different; workers are more likely to set aside quality time to recover from childbirth or bond with a new child than they are to lay on a beach or tour a European city. But an unlimited offering puts a great deal of uncertainty on employees. For workers, taking time off becomes more like taking someone up on a favor rather than accepting a benefit you are entitled to.

“Having a set amount of time crates a more tangible expectation or norm. Unlimited policies can seem amorphous,” says Vicki Shabo, vice president at the National Partnership for Women & Families.

In an ideal world, new parents would decide how many days to take off in the vacuum of their own personal lives, but it’s silly to assume that such a safe space exists; it’s tainted by concerns about missing too many meetings, returning to too many unanswered emails, and it prompts comparisons to other new parents who missed fewer days following their child’s birth. As if new moms and dads didn’t have on their minds, they’re now under pressure to calculate the exact number of days they’ll need to adapt to parenthood and then justify that decision to their employer.

Netflix should be commended for its ample policy. New parents should receive more paid time off than they’re currently getting. But if a company is going to be so generous, it should offer precise guidance to employees.

“Where the rubber meets the road is whether people feel comfortable using the time they’re given,” Shabo says. There needs to be “a cultural expectation that they can use the time without their career track being penalized.”

A Netflix spokesperson said the company communicated the new policy with employees before it posted it publicly. The company is providing managers with tools to help discuss the policy with employees, and its leaders will “take an active role” to help managers and employees adapt, she said.

At the very least, Netflix has articulated “a cultural aspiration that acknowledges that people have personal lives and professional lives,” Shabo says. “To the extent that they can ameliorate the clash between the two, then the new the policy purports to stand out as a new standard.”