From free snack bars to fridges stocked with chilled beers, gym memberships and time off for travel, more businesses are offering corporate wellness perks to attract and retain employees.

They are eye-catching offers meant to boost recruitment and staff retainment. “When we’ve got a lot of competition for jobs, more perks come into play,” explains Susan Cartwright, professor of organisational psychology and wellbeing at Lancaster University. “When there isn’t, these perks disappear.”

Current job market dynamics mean employees can call the shots. We’re quicker to shun jobs that don’t work for us and more likely to career hop than in the past. Data collected by the United States Bureau of Labor Statistics shows that men between the ages of 25 and 34 spend on average just 2.9 years with each employer – a drop from 1983, when the average tenure was 3.2 years.

Savvy employers now dangle a raft of benefits in front of workers to keep them in place. Many also offer incentives meant to improve wellbeing – which is important as mental health becomes more of an issue for companies. But which benefits work and which ones don’t? And if a work perk is a gimmick, what is a boring – but effective – alternative?

Taking a break

Some of the biggest, self-consciously “coolest” businesses including Netflix and the Virgin Group offer unlimited holidays to employees, allowing them to take as much time off work as they’d like. Where big firms lead, others follow: 5% of companies offer unlimited leave, according to the Society for Human Resource Management (SHRM), an American HR association, up from just 1% in 2014.

So-called unlimited or “open” leave boosts staff self-worth in many ways, says Suzanne Goulden of SHRM. “Employees really appreciate being treated like the adults they are and for the most part being allowed to determine their leave needs.”

But the effects are unproven. “From a PR point of view, it’s great,” says Cary Cooper, professor of organisational psychology at Manchester Business School. But he adds: “We don’t know if people take it up.”

Taking holiday is beneficial for both businesses and workers: a 2015 study found that employees who take all their mandated holiday time improve their chances of getting promoted and a pay rise by 6.5%, compared to those who leave 11 or more days of their entitlement untouched.

However, as humans we like rules, and instigating an all-you-can-take approach to holidays at work can cause employees anxiety. “You know structurally what’s happening when you’re told you get four or five weeks off,” says Cooper. Different line managers may have different approaches to taking time off, and employees can’t decipher that.