It works as long as you have a culture where people don't abuse it. It's not workable if people think it's acceptable to disappear with some critical information only in their head and screw their coworkers. Document stuff. Set deadlines in advance, and expect people to meet them. Have a team that collaborates and is considerate to their peers. If people do this, nobody is counting how many days they're out.
I'd rather work at an unlimited PTO company with reasonable people than one with a generous allowance where people are always scheming to use it as a weapon.
