Some companies have a new perk for employees in the form of "unlimited time off, as long as you get your work done" 1. While at first glance this would seem to be a really nice benefit, I would counter that instead, because of the "get your work done" caveat, it penalizes the busiest and possibly overworked employees. These employees are less able to take time without impacting/blocking others. I would suggest an alternative PTO policy that includes the previous "unlimited" PTO, but extends with a "required" PTO. This would be a set period each year that each employee is required to take PTO. This would insure busy teams/employees can take the time they need, force the company to better plan and properly staff each team.

1: I work for a company with this policy. This is not a rant against them, just an observation