Are you under the impression that taking less days off than you're allotted will show your boss what a great employee you are? Think again: New EY (formerly Ernst & Young) research shows that people who take all of their vacation days get better performance reviews. "In the U.S. and Canada, for each 10 vacationhours a person took, we found on average that performance reviews were 8 percent higher," said Maryella Gockel, flexibility strategy leader at EY. What’s more, vacation also helped slow turnover, with every 40 hours of free time extending an employee’s stay at the company by eight months, Gockel told CNBC.